chambers of different size and form. Both proximal chambers kidney-shaped,
with subregular, circular, hexagonally framed pores, about as broad as the
bars. All the following chambers hemispherical, with irregular, roundish
pores; at the base of every chamber a circle of ten to twelve larger square
pores. The beams between these latter are prolonged into free radial
spines, twice as thick as the bars. Therefore every chamber is surrounded
by a circle of radial spines, like those of _Panicium coronatum_ (Pl. 40,
fig. 4). Both medullary shells lenticular.
_Dimensions._--Length of the six-chambered cortical shell 0.3, greatest
breadth 0.08, pores and bars of both proximal chambers 0.01; pores of the
other chambers 0.002 to 0.008; square pores 0.02, bars 0.005; length of the
coronal spines 0.03, thickness 0.01.
_Habitat._--Indian Ocean, Madagascar, Rabbe.
Subgenus 4. _Ommatacantha_, Haeckel.
_Definition._--Surface of the shell smooth or spiny, on the poles of the
main axis occur two strong opposite polar spines.
7. _Ommatocampe amphilonche_, n. sp.
Cortical shell composed of six kidney-shaped chambers of nearly the same
size and structure; every chamber twice as broad as long, with four to five
transverse rows of irregular, roundish pores, once to four times as broad
as the bars. Both medullary shells lenticular. Surface of the cortical
shell covered with bristle-like spines. On both poles of the main axis one
larger, strong, conical spine, about half as long as this axis, and on the
base as broad as the inner medullary shell. (Resembles on the whole
_Desmartus larvalis_, Pl. 40, fig. 12, but without external mantle, and
with two solid polar spines instead of the polar tubes.)
_Dimensions._--Length of the six-chambered cortical shell 0.24; greatest
breadth of each chamber 0.08; pores 0.002 to 0.08, bars 0.002; length of
the polar spines 0.12, basal thickness 0.02.
_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.
Genus 170. _Ommatartus_,[209] Haeckel, 1881, Prodromus, p. 463.
_Definition._--#Zygartida# with simple cortical shell and double medullary
shell, with two hollow fenestrated tubes, opposite on both poles of the
main axis.
The genus _Ommatartus_ differs from _Ommatocampe_ by the development of two
hollow fenestrated tubes on both poles of the main axis, and bears
therefore the same relation to it as _Cannartidium_ to _Cyphonium_. The
former two genera differ from the two latter by the augmentation of the
chambers of the cortical shell.
{396}1. _Ommatartus amphicanna_, n. sp.
Cortical shell with spiny surface, composed of six chambers of equal size
and kidney-shaped; every chamber with four to five transverse rows of
irregular, roundish pores, twice to three times as broad as the bars. Both
medullary shells lenticular. Polar tubes conical, about as long as one
chamber, with smaller pores. Both medullary shells spheroidal, more or less
compressed. (Resembles _Desmartus larvalis_, Pl. 40, fig. 12, but is
without the external shell.)
_Dimensions._--Length of the six-chambered cortical shell 0.24; greatest
breadth of each chamber 0.07; pores 0.008 to 0.012, bars 0.004; length of
the polar tubes 0.04 to 0.05, basal thickness 0.02.
_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925
fathoms.
2. _Ommatartus amphisiphon_, n. sp.
Cortical shell with spiny surface, composed of six or eight chambers of
different size and form. Both proximal chambers kidney-shaped, each with
five to six transverse rows of irregular, polygonal pores, three to four
times as broad as the bars. The other (four to six) chambers somewhat
smaller, more hemispherical, with smaller, irregular pores, but on the base
of each a circle of ten to twelve larger square pores. Polar tubuli
prismatic, about half as long as the main axis, with prominent edges and
longitudinal rows of smaller pores between them. Both medullary shells
lenticular. (Resembles closely _Panarium tubularium_, Pl. 40, fig. 9, but
with six to eight chambers instead of four, and with longer tubuli.)
_Dimensions._--Length of the six-chambered cortical shell 0.26; greatest
breadth of the proximal chambers 0.09, of the distal chambers 0.07; pores
of the former 0.01, of the latter 0.004; large square pores 0.013, bars
0.003; length of the polar tubes 0.1 to 0.12, thickness 0.02.
_Habitat._--South Pacific, Station 297, depth 1775 fathoms.
3. _Ommatartus amphobolus_, n. sp.
Cortical shell with spiny surface, composed of six chambers of different
size and form. Both proximal chambers kidney-shaped, with four to five
transverse rows of subregular, circular pores, twice as broad as the bars.
Both middle chambers cap-like, with a basal circle of ten to twelve larger
square pores, and small roundish pores on the cap. Both distal chambers
smaller, conical, with very small roundish pores. Polar tubuli conical,
nearly half as long as the main axis, also with very small pores. Both
medullary shells lenticular.
_Dimensions._--Length of the six-chambered shell 0.28, greatest breadth
0.08; pores of the proximal chambers 0.01, bars 0.005; pores of the distal
chambers and the polar tubes 0.002 to 0.004, bars 0.002; length of the
polar tubes 0.13, basal thickness 0.03.
_Habitat._--North Pacific, Station 253, depth 3125 fathoms.
Genus 171. _Desmocampe_,[210] n. gen.
_Definition._--#Zygartida# with double cortical shell and double medullary
shell, without polar tubes.
{397}The genus _Desmocampe_ differs from _Ommatocampe_ in the duplication
of the jointed cortical shell; the radial spines, which start from the
surface of the inner cortical shell, are connected one with another by
transverse communicating branches which form an outer envelop around it;
but this reticulated mantle is commonly not quite perfect and more or less
irregular.
1. _Desmocampe catenula_, n. sp.
Inner cortical shell with six to eight chambers of the same size and form.
Every chamber kidney-shaped, with three to four transverse rows of
circular, subregular pores, twice as broad as the bars. Outer cortical
shell cylindrical, hemispherical at both poles, with smooth surface and
irregular, roundish pores of very different size. Distance between the two
cortical shells equals the diameter of the outer medullary shell, which,
like the inner, is spherical. (Resembles Ommatocampe polyarthra, Ehrenberg,
1872, _loc. cit._, Taf. vi, fig. 9, but differs in the external mantle.)
_Dimensions._--Length of the six-chambered inner cortical shell 0.16, of
the outer 0.21; greatest breadth of each chamber of the former 0.05, of the
latter 0.09; pores of the inner 0.006, bars 0.003; pores of the outer 0.002
to 0.008, bars 0.002.
_Habitat._--North Pacific, Station 237, off Japan, surface.
2. _Desmocampe tænioides_, n. sp.
Inner cortical shell with six to ten chambers of nearly the same size and
form; the distal chambers somewhat smaller. Every chamber kidney-shaped,
with four to five transverse rows of irregular roundish pores, twice to
three times as broad as the bars. Outer cortical shell cylindrical,
hemispherical at both poles, with spiny surface; its pores like those of
the inner, but the bars between them much thinner. Distance between the two
cortical shells equals the diameter of the outer medullary shell. Both
medullary shells lenticular. (Resembles _Desmartus larvalis_, Pl. 40, fig.
12, but is without polar tubes.)
_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of
the outer 0.3; greatest breadth of the former 0.07, of the latter 0.11;
pores 0.005 to 0.012; bars of the inner shell 0.004, of the outer 0.001.
_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.
3. _Desmocampe aphrodite_, n. sp.
Inner cortical shell with six to ten chambers of different size and
structure. Both proximal chambers kidney-shaped, with five to six
transverse rows of subregular, circular, hexagonally-framed pores, twice as
broad as the bars. All following chambers cap-like, with much smaller,
irregular, roundish pores, on the base of each a circle of ten to twelve
large square pores. Outer cortical shell cylindrical, on both poles
hemispherical, with spiny surface and very delicate network of small
polygonal pores. Both medullary shells spherical. (The inner cortical shell
of this species resembles that of _Ommatocampe nereis_, Pl. 40, fig. 10;
the outer that of _Cyphocolpus virginis_, Pl. 40, fig. 11.)
{398}_Dimensions._--Length of the six-chambered internal cortical shell
0.25, of the outer 0.3; greatest breadth of the former 0.08, of the latter
0.12; pores of the proximal chambers of the inner shell 0.01, bars 0.005;
pores of the distal chambers 0.003 to 0.005, square pores 0.02, bars 0.003;
pores of the external cortical shell 0.002 to 0.006, bars 0.001.
_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.
4. _Desmocampe atractus_, n. sp.
Inner cortical shell with six chambers of very different size and
structure. Both proximal chambers kidney-shaped, with seven to eight
transverse rows of subregular, roundish pores, twice to three times as
broad as the bars. Both middle chambers cap-like, on the base with a circle
of eight to ten very large square pores, on the distal cap with small
irregular, roundish pores. Both distal chambers conical, also with small
irregular, roundish pores. Outer cortical shell spindle-shaped, inflated in
the equatorial zone, tapering conically towards both poles, with very
delicate network of small roundish pores and thin bars. Surface covered
with innumerable very small spines. Both medullary shells lenticular.
(Resembles very much _Peripanartus atractus_, Pl. 40, fig. 7, but differs
in the number of the chambers and their proportion to the outer mantle,
which envelops spindle-like all six chambers.)
_Dimensions._--Length of the six-chambered internal cortical shell 0.27, of
the outer 0.32; greatest breadth of the former 0.09, of the latter 0.15;
pores of the inner cortical shell (on an average)--proximal chambers 0.008,
middle chambers 0.02, distal chambers 0.004, bars 0.004; pores of the outer
cortical shell 0.002 to 0.004, bars 0.002.
_Habitat._--North Pacific, Station 241, depth 2300 fathoms.
Genus 172. _Desmartus_,[211] n. gen.
_Definition._--#Zygartida# with double cortical shell and double medullary
shell, with two hollow fenestrated tubes, opposite on both poles of the
main axis.
The genus _Desmartus_ differs from _Desmocampe_ by the development of two
hollow fenestrated tubes, opposite on both poles of the main axis, and
bears therefore the same relation to it as _Ommatartus_ to _Ommatocampe_.
Both the former genera can be produced from the two latter by duplication
of the cortical shell.
1. _Desmartus larvalis_, n. sp. (Pl. 40, fig. 12).
_Zygartus larvalis_, Haeckel, 1881, Prodromus et Atlas (pl. xl, fig. 12).
Inner cortical shell composed of six kidney-shaped chambers of nearly the
same size and structure; every chamber twice as broad as long, with four to
five transverse rows of irregular, roundish pores, twice to five times as
broad as the bars; the basal pores of the distal chambers {399}somewhat
larger and more square. Outer cortical shell cylindrical, hemispherical at
both poles, with irregular, polygonal pores, on an average twice as large
as those of the inner, but the bars between them much thinner. Outer
surface spiny. Both medullary shells lenticular. Polar tubes conical, a
little longer than one internal chamber, as broad at the base as the inner
medullary shell. Sometimes the tubes exhibit prominent edges (as in the
lower spine of fig. 12); the pores of these are very small, and roundish.
_Dimensions._--Length of the six-chambered internal cortical shell 0.23, of
the external 0.3; greatest breadth of the former 0.07, of the latter 0.11;
pores of the inner shell 0.004 to 0.01, of the outer 0.01 to 0.02; bars of
the former 0.002, of the latter 0.001; length of the polar tubes 0.05,
basal thickness 0.02.
_Habitat._--North Pacific, Station 241, depth 2300 fathoms.
2. _Desmartus tubulatus_, n. sp.
Inner cortical shell composed of six to ten kidney-shaped chambers,
tapering in size towards both poles, every chamber with six to seven
transverse rows of irregular, roundish pores, twice to six times broader
than the bars. Outer cortical shell spindle-shaped, in the equatorial zone
inflated, tapering towards both poles, its network similar to the inner,
only more delicate. Polar tubes conical, twice as long as an inner chamber,
as broad at the base as the outer medullary shell. Both medullary shells
lenticular.
_Dimensions._--Length of the six-chambered internal cortical shell 0.25, of
the external 0.32; greatest breadth of the former 0.08, of the latter 0.12;
pores of the inner shell 0.002 to 0.012, of the outer 0.003 to 0.01; bars
of the former 0.002, of the latter 0.001; length of the polar tubes 0.07,
basal thickness 0.03.
_Habitat._--North Pacific, Station 256, depth 2950 fathoms.
Genus 173. _Zygocampe_,[212] n. gen.
_Definition._--#Zygartida# with triple (or multiple) cortical shell and
double medullary shell, without polar tubes.
The genus _Zygocampe_ differs from _Desmocampe_ and _Ommatocampe_ by the
multiplication of the cortical shell, which is composed of three or more
concentric envelopes. The three mentioned genera form therefore a
phylogenetic series, produced by the concentric increase on the outside of
the jointed cortical shell. Commonly the second cortical shell is not as
complete as the first (or innermost), and the third (or outermost) is yet
more incomplete. Rarely the number of the concentric cortical shells
surpasses three.
1. _Zygocampe pupula_, n. sp.
Inner cortical shell with six to twelve chambers of nearly the same size
and form. Every chamber kidney-shaped, with four to five transverse rows of
circular, subregular pores, twice as {400}broad as the bars. Middle
cortical shell cylindrical, hemispherical at both poles, with subregular
circular pores somewhat smaller than those of the inner; the bars also
thinner. Outer cortical shell of the same form as the middle, but with very
delicate network, and quite irregular, roundish pores and very thin bars.
Surface quite smooth. Both medullary shells lenticular. (May be regarded in
a phylogenetic as well as an ontogenetic sense, as the further
developmental form of _Desmocampe catenula_ and _Ommatocampe polyarthra_.)
_Dimensions._--Length of the six-chambered inner cortical shell 0.17, of
the middle 0.22, of the outer 0.27; greatest breadth of the first 0.05, of
the second 0.09, of the third 0.12; pores of the inner cortical shell
0.005, of the middle 0.004, of the outer 0.003 to 0.012; bars of the first
0.003, of the second 0.002, of the third 0.001.
_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.
2. _Zygocampe corasium_, n. sp.
Inner cortical shell with six to eight chambers of different size and form.
Both proximal chambers kidney-shaped, with five to six transverse rows of
subregular, circular, hexagonally framed pores, twice as broad as the bars.
All following chambers cap-like, the distal somewhat smaller; their pores
much smaller, irregular, roundish; only at the base of each chamber a
circle of ten to twelve large square pores. Middle cortical shell
cylindrical, in the equatorial zone a little constricted, hemispherical at
both poles, with irregular delicate network of roundish, polygonal meshes.
Outer cortical shell of the same form as the middle, but with a very
delicate and quite irregular network of polygonal meshes. Commonly this
outer mantle is incomplete, and sometimes interwoven in a spongy manner
with the middle (or also with the inner). Surface covered with many
irregular, thin, bristle-like spines. Both medullary shells lenticular.
(May be considered in a phylogenetic and ontogenetic sense as a further
developmental stage of _Desmocampe aphrodite_ and _Ommatocampe nereis_, Pl.
40, fig. 10.)
_Dimensions._--Length of the six-chambered inner cortical shell 0.24, of
the middle 0.3, of the outer 0.36; greatest breadth of the first 0.08, of
the second 0.12, of the third 0.16, pores of the first (on an average)
0.005 to 0.02, of the second 0.003 to 0.015, of the third 0.01 to 0.05;
bars corresponding 0.005 or 0.003 or 0.001.
_Habitat._--North Pacific, Station 253, depth 3125 fathoms.
3. _Zygocampe chrysalidium_, n. sp. (Pl. 40, fig. 13).
Inner cortical shell with six to eighteen chambers of different size and
form. Both proximal chambers kidney-shaped, with six to seven transverse
rows of subregular, circular pores, three to four times as broad as the
bars. All following chambers with more irregular pores, with a circle of
ten to twelve larger square pores at the base. Middle cortical shell with
smaller, irregular, roundish pores. Outer cortical shell with larger
polygonal, quite irregular pores. Both outer shells appear commonly
incomplete or somewhat irregularly developed, and sometimes in a spongy
manner interwoven with one another. Surface covered with irregular,
bristle-like spines. Both medullary shells spherical. The breadth of the
chambers decreases gradually towards both poles, so that the whole shell
assumes a spindle form. Sometimes on both poles is developed a short
conical {401}polar tube (in fig. 13 only on the upper pole), and so this
species is transformed into _Zygartus chrysalis_.
_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of
the middle 0.3, of the outer 0.35; greatest breadth of the first 0.07, of
the second 0.11, of the third 0.14; pores (on an average) 0.01 (0.002 to
0.02), bars 0.002 to 0.005.
_Habitat._--Pacific, central area, Stations 272 to 274, depth 2350 to 2750
fathoms.
Genus 174. _Zygartus_,[213] Haeckel, 1881, Prodromus, p. 463.
_Definition._--#Zygartida# with triple (or multiple) cortical shell and
double medullary shell, with two hollow fenestrated tubes, opposite on both
poles of the main axis.
The genus _Zygartus_ differs from Zygocampe by the development of two
hollow fenestrated tubes, on the two opposite poles of the main axis. It
exhibits therefore to the latter the same relation that _Desmartus_ does to
_Desmocampe_ and _Ommatartus_ to _Ommatocampe_; it differs from these by
the multiplication of the cortical shell, which is composed of at least
three concentric envelopes.
1. _Zygartus doliolum_, n. sp.
Inner cortical shell composed of six (or more) kidney-shaped chambers, all
nearly of the same size and structure, every chamber with four to five
transverse rows of irregular, roundish pores, twice to four times as broad
as the bars; the basal pores scarcely larger than the apical pores. Middle
cortical shell nearly of the same structure as the inner, only the pores
larger and the bars thinner. Outer cortical shell cylindrical,
hemispherical at both poles, its network very delicate, with large
irregular, polygonal pores, and very thin bars between them; its surface
covered with thin bristle-like spines. Both medullary shells lenticular.
Polar tube cylindrical, with conical apex, and with very small pores; its
length equals the breadth of two internal chambers, its breadth that of the
inner medullary shell. (This species appears to be a further developed form
of _Ommatocampe annulata_ and _Desmartus larvalis_, Pl. 40, fig. 12.)
_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of
the middle 0.3, of the outer 0.35; greatest breadth of the first 0.07, of
the second 0.11, of the third 0.15; pores of the inner shell 0.005 to 0.01,
of the middle 0.003 to 0.007, of the outer 0.008 to 0.02; bars of the first
0.002, of the second and third 0.001; length of the polar tubes 0.15, basal
thickness 0.02.
_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.
2. _Zygartus chrysalis_, n. sp. (Pl. 40, fig. 13).
Inner cortical shell composed of six to twenty (commonly eight to twelve)
chambers of different size and form. Both proximal chambers nearly
hemispherical, with spiny surface and subregular, {402}circular pores,
three to four times as broad as the bars. All following chambers cap-like,
tapering towards both poles, with more irregular, roundish pores, with a
circle of ten to twelve larger square pores at the base. Middle cortical
shell with smaller roundish pores. Outer cortical shell with larger
polygonal, quite irregular pores. Both medullary shells lenticular. Polar
tubes conical or cylindrical with conical apex, of very variable length,
sometimes not longer than one internal chamber, at other times twice to
four times as long (in the figured specimen not fully developed, as also a
part of the shells). Differs from _Zygocampe chrysalis_ only by the
production of polar tubes.
_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of
the middle 0.3, of the outer 0.35; greatest breadth of the first 0.07, of
the second 0.11, of the third 0.14; other measures the same as in
_Zygocampe chrysalis_; length of the tubes 0.05 to 0.12 or more.
_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925
fathoms.
----
Suborder V. DISCOIDEA, Haeckel (Pls. 31-38, 41-48).
_Discida_ vel _Discoidea_, Haeckel, 1862, Monogr. d. Radiol., pp. 56,
476.
_Discoida_, _Discoidea_, _Discida_, Haeckel, 1878, Protistenreich, p.
103.
_Definition._--SPUMELLARIA with discoidal or lenticular central capsule
(often with radial prolongations, rarely allomorphic); with discoidal or
lenticular fenestrated siliceous shell (often with radial spines or
fenestrated arms, rarely allomorphic). Growth reduced or diminished in the
direction of one dimensive axis.
The section #Discoidea# comprises those SPUMELLARIA in which the
fenestrated shell is more or less discoidal or lenticular, flattened or
compressed in the direction of one axis. The geometric fundamental form of
the latticed shell, which in the #Sphæroidea# is a sphere, here becomes a
flat disk, like a medal, or a biconvex lens, sometimes also a biconcave
lens. The #Discoidea# can be derived from the #Sphæroidea# by shortening of
one axis. This shortened vertical axis is the main axis of the disk; both
its poles are constantly equal. Perpendicular to this axis is the
equatorial plane of the disk by which it becomes divided into equal halves.
In the simplest forms of #Discoidea# all axes of this horizontal equatorial
plane (all "equatorial axes" or "cross axes") are equal; in the most of the
genera and species these cross axes are different, so that rays of stronger
growth ("perradii") alternate with rays of weaker growth ("interradii").
The number of these cross axes distinguishable is commonly two to four,
rarely more. In the direction of these are developed either radial marginal
spines or spongy arms.
The order #Discoidea# was founded in my Monograph (1862, p. 476) as the
family "Discida" (Radiolaria with flat discoidal or biconvex lenticular
shell), comprising the {403}"_Calodictya_ and _Lithocyclidina_" of
Ehrenberg and a great part of his "_Haliommatina_." As three different
subfamilies of that family I separated the Coccodiscida (with five genera),
the Trematodiscida (with seven genera), and the Discospirida (with two
genera; Monogr. d. Radiol., p. 485). A fourth group of #Discoidea# was
constituted by the Spongodiscida (with eight genera, including the
_Spongocyclida_), which at that time I united with the Spongurida, because
of their spongy structure (_loc. cit._, p. 452).
As the number of fossil #Discoidea# found in the Tertiary rocks of Barbados
and of the Mediterranean shores (Sicily and Greece) is comparatively very
large, we find even in the first system of Polycystina of Ehrenberg (1847),
not less than twelve genera distinguished, viz., six _Calodictya_, two
_Haliommatina_, and four _Lithocyclidina_ (Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, 1847, p. 53). The whole number of Radiolarian genera
distinguished in that first system was forty-four. The diagnoses of them
given by Ehrenberg were as usual very insufficient. The characters of the
three families given by him were the following:--_Calodictya_--"Testarum
intus spongiosarum et nucleo destitutarum orbes; _Haliommatina_--Testæ
subglobosæ nucleus radiatus; _Lithocyclidina_--Testarum disci in media
parte nucleati margine celluloso." In the latest work of Ehrenberg (1875,
p. 157) the same system was repeated, but some new genera added; and
thirty-eight different species, appertaining to the #Discoidea#, were
figured in the same work (Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Tafs.
xx.-xxx.).
Richard Hertwig, 1879, in his excellent work, Der Organismus der
Radiolarien (pp. 57-68), gave a detailed description of the skeleton of
some #Discoidea#, and arrived at the conclusion that this whole family had
a spirally constructed skeleton, and should therefore be derived from the
Lithelida. But this conclusion is certainly erroneous, and in my opinion
the whole explanation of that spiral structure, and of its signification in
the development of #Discoidea#, is the weakest part of that otherwise very
important work.
In my Prodromus (1881, p. 456) I gave a provisional system of the #Discida#
or #Discoidea# from the immense quantity of new material collected by the
Challenger, and could distinguish not less than eighty-four genera. This
number is from subsequent research only augmented by seven, so that in the
following pages ninety-one genera with five hundred and one species are
described. In the Prodromus I had disposed them in four different families,
which number is now increased to six. These six families can be again
disposed in two main groups or sections, the #Phacodiscaria# and the
#Cyclodiscaria#, each section with three families.
The #Phacodiscaria# are characterised by the possession of a typical
"phacoid shell," and contain the three families Cenodiscida, Phacodiscida,
and Coccodiscida. On the other hand, the #Cyclodiscaria# are distinguished
by the absence of such a "phacoid shell," and contain the three families
Porodiscida, Pylodiscida, and Spongodiscida. Both sections exhibit an
analogous development.
{404}The #Cenodiscida# (Pl. 48, figs. 1-3) open the series of the
#Discoidea# as their simplest forms; a discoidal or lenticular simple
lattice-shell encloses a central capsule of the same form, and is separated
from it by the calymma or jelly-veil. The common ancestral form of this
family is _Cenodiscus_, without radial marginal spines; it can be derived
from _Cenosphæra_ in the most simple way, by flattening in one axis. If on
the equatorial margin of the lens a peculiar solid girdle be developed, we
obtain _Zonodiscus_; in all other genera of the Cenodiscida radial spines
are developed on the margin. As the simple lenticular cortical shell of
_Cenodiscus_, in which the central capsule is enclosed, is most
characteristic not only of this family, but also of the two following
families, we call it the phacoid shell (that is, a lenticular extracapsular
or cortical lattice-shell).
The #Phacodiscida# (Pls. 31-35), the second family, have the same
extracapsular "phacoid shell" as the Cenodiscida, but differ from these by
the possession of one or two intracapsular concentric medullary shells,
which are connected with the former by radial beams, perforating the
lenticular central capsule. The radial beams are commonly numerous, and
arranged in two opposite bunches around the shortened main axis. But often
also besides these occur other longer radial beams, situated in the
equatorial plane; the number of these is commonly four, and they form a
regular rectangular cross, lying opposite in pairs in two equatorial
diameters, perpendicular one to another. In the simplest genera of this
family (the _Sethodiscida_) the equatorial margin of the phacoid shell is
simple or surrounded by a solid smooth girdle; in all other genera are
developed on the margin solid radial spines lying in the equatorial plane,
either regularly disposed in a somewhat constant number (two to eight,
_Heliosestrida_), or irregularly disposed, in a larger and more variable
number (ten to twenty or more, _Heliodiscida_).
The #Coccodiscida# (Pls. 36-38) form a third family of the #Discoidea#,
directly associated with the Phacodiscida; both have the same
characteristic extracapsular "phacoid shell," which is connected by radial
beams with a simple or double, intracapsular medullary shell. But whilst in
the foregoing family the equatorial margin of the phacoid shell is simple
or only armed with radial spines, in the Coccodiscida it is surrounded by
peculiar concentric chambered girdles, or rings, which resemble those of
the following family, the Porodiscida. Each of these "chambered girdles" is
composed of a circular ring in the equatorial plane, a variable number of
radial beams dividing it into incomplete chambers, and two porous
cover-plates or "sieve-plates," covering the upper and lower face of the
disk. These sieve-plates may be regarded as incomplete lenticular cortical
shells, which are only developed in the peripheral part of the disk, whilst
their central part is represented by the only complete cortical shell, the
"phacoid shell." The number of these concentric chamber-girdles amounts to
from one to ten or more. The margin of the disk is either simple
(Lithocyclida) or armed with radial spines (Stylocyclida), or provided with
two to five chambered radial arms (Astracturida); the structure of the arms
is the same as that of the girdles.
{405}The #Porodiscida# (Pls. 41-47), the largest family of all #Discoidea#,
begins the series of #Cyclodiscaria#, or those #Discoidea# in which there
is no "phacoid shell," but a small simple central chamber surrounded by a
number of small latticed chambers of nearly the same size and form. In the
Porodiscida these chambers are arranged in complete circular concentric
rings or spiral convolutions; in the small family of Pylodiscida the
central chamber is surrounded by three radial arm-chambers separated by
three open spaces; in the third family of #Cyclodiscaria#, the
Spongodiscida, all the chambers are arranged more or less irregularly, and
the whole disk becomes spongy; also the surface of the disk is spongy,
whilst in both former families it is covered by two regular even porous
plates or "sieve-plates." Probably all #Cyclodiscaria# can be derived
phylogenetically from _Archidiscus_, a very small and simple lenticular
disk, which is composed of a small spherical latticed central chamber and
of a single concentric chambered ring or girdle; the margin of this ring is
connected with the central chamber by a variable number of radial beams.
This _Archidiscus_ can be derived either from _Saturnalis_ (Pl. 13, fig.
16.) by the development of lattice-work between the equatorial ring and
both polar faces of the concentric central chamber, or from _Sethodiscus_
(Pl. 33, figs. 1-3) by flattening of the lenticular shell, so that the
enclosed inner medullary shell (the central chamber) meets the outer
phacoid shell at both poles.
The Porodiscida are commonly flat or biconvex (rarely biconcave) disks, the
central chamber of which is surrounded not by a single, but by a variable
number (commonly three to six) of concentric chambered girdles or rings;
they arise from _Archidiscus_ by apposition of new concentric chambered
rings around the first ring, all lying in the equatorial plane. Afterwards
the disk often becomes thickened by apposition of concentric chamber-rings
on both flat sides also, so that two to four or more layers are stratified
one over the other. The circular concentric rings often become interrupted,
or spirally convoluted (wholly or partially); also the chambers sometimes
become irregularly crowded. But in all cases both surfaces of the disk
(upper and lower) continue to be porous plates or sieve-plates, at least in
the centre, but they never become spongy.
The margin of the disk exhibits in the Porodiscida a great variety of
different forms, serving for distinction of subfamilies and of genera. In
the Trematodiscida the margin remains quite simple, as in the Archidiscida,
or is only surrounded by a hyaline equatorial girdle. In the Ommatodiscida
it is distinguished by one or two peculiar oscula, surrounded by a corona
of spines. The Stylodictyida are distinguished by a number of solid radial
spines, and the Euchitonida by a number of chambered, or spongy, radial
arms, arising from the margin of the disk and lying in the equatorial
plane. The variety of these radial marginal appendages is in the
Porodiscida much greater than in the Coccodiscida.
The #Pylodiscida# (Pl. 48, figs. 12-20) represent a new, small, but very
remarkable family of #Discoidea#, all triradial, and distinguished by the
peculiar formation of {406}large open spaces in the latticed discoidal
shell, which reappear in a similar shape among the #Larcoidea# in the
Pylonida (_Tetrapyle_, &c.). We get the best understanding of this peculiar
formation if we return to _Archidiscus_, probably the common ancestral form
of all #Cyclodiscaria#, of the Porodiscida as well as of the Pylodiscida
and Spongodiscida. In some species of _Archidiscus_ (_Archidiscus
hexoniscus_, _Archidiscus pyloniscus_, &c.) the small lenticular shell is
composed of a spherical latticed central chamber and of a concentric
equatorial girdle composed of six such chambers, either all six equal, or
alternately larger and smaller. This latter form is nearly identical with
_Triodiscus_, and if we imagine the lattice-work of only three
ring-chambers complete, whilst that of the three alternating chambers is
reduced to the marginal ring, we get _Triopyle_, by loss of this ring
_Triolene_ (a disk composed of four simple lattice-chambers, lying in one
plane, three radial around one central spherule). The genera mentioned form
together the subfamily of Triopylida. In the second subfamily, Hexapylida,
the same formation is doubled; here three double arm-chambers are separated
by three double spaces (two in each radius). Also here the three distal
spaces may be either quite open (_Pylolena_), or half closed by the
marginal girdle (_Hexapyle_), or quite loosely latticed (_Pylodiscus_). If
the margin of this latter form become surrounded by a perfect chambered
equatorial girdle, we get _Discozonium_, and if this acquire a peculiar
marginal ostium (surrounded by a corona of spines) we arrive at
_Discopyle_. These two latter genera form the third subfamily, the
Discopylida. The eight genera of Pylodiscida represent therefore a
continuous phylogenetic series.
The #Spongodiscida# are the sixth and last family of the #Discoidea#,
differing from the five other families in the irregular, spongy structure
of the discoidal skeleton; both surfaces of the flat disk (upper and lower)
are here principally covered with a rough, spongy framework, whilst in the
five other families they are covered by the flat and smooth porous plates
or sieve-plates. Nevertheless there is no sharp boundary between the
Spongodiscida and the closely allied Porodiscida. In these latter also the
discoidal shell becomes often more or less spongy (mainly in the peripheral
part, _e.g._, in _Myelastrum_, Pl. 47); but at least the central part of
the disk here remains constantly covered by sieve-plates. The massive
skeleton of the Spongodiscida is either of perfectly irregular structure,
only composed of innumerable fine branched siliceous threads, interwoven in
all possible directions; or only the outer part of the disk is composed of
such spongy framework, whilst the central part is more or less distinctly
composed of concentric chambered rings, as in the Porodiscida. These latter
forms indeed exhibit an immediate transition to this family, and were
formerly (in 1862) separated by me as Spongocyclida. Also the polymorphous
shape of the disk margin in the Spongodiscida is quite analogous to that of
the Porodiscida. Whilst in the first subfamily, the Spongophacida, the
margin is quite simple; in the second, the Spongotrochida, it is armed with
solid radial spines; and in the third, the Spongobrachida, it is provided
with two, three, {407}or four spongy, radial arms--the former as well as
the latter lying in the equatorial plane of the disk, either regularly or
irregularly disposed.
_The Equatorial Margin_ of the lenticular disk exhibits in all six families
of #Discoidea# similar characters, mainly serving for the distinction of
subfamilies and genera. In the most primitive genera of all six families
the margin is simple, without radial prolongations (spines or arms); it is
quite simple in _Cenodiscus_, _Sethodiscus_, _Phacodiscus_, _Lithocyclia_,
_Coccodiscus_, _Archidiscus_, _Porodiscus_, _Pylodiscus_, and
_Spongodiscus_. In some genera the simple margin of the lenticular disk is
bordered and surrounded by a thin, hyaline, equatorial girdle of silex,
either quite solid or slightly porous (_Zonodiscus_, _Periphæna_,
_Perizona_, _Perichlamydium_, and _Spongophacus_).
A quite peculiar and remarkable character of few genera is the development
of one or two oscula, larger marginal openings, which are surrounded by a
corona of spines, and probable are fit for the issue a peculiar bunch of
pseudopodia or of a "sarcode flagellum." Such oscula occur only in two
families of #Cyclodiscaria#; in the Porodiscida and Pylodiscida; in the
former _Ommatodiscus_, in the latter _Discopyle_ (Pl. 48, figs. 19, 20) is
distinguished by a single marginal osculum; besides this, in the former
occurs _Stomatodiscus_, with two such oscula, opposite on the poles of one
axis (Pl. 48, fig. 8). These oscula may be compared with the similar polar
formations in some Ellipsida (_Lithomespilus_) and in many Cyrtoidea; but
they do not prove a nearer affinity with the latter, and are only
analogous, not homologous.
_Radial Spines_ occur on the margin in the equatorial plane of the
#Discoidea# in the greatest variety of number, form, size, and disposition.
If the number be low (between two and eight) they are commonly regularly
disposed; if the number be larger (ten to twenty or more) their disposition
becomes commonly more or less irregular. The regular disposition is of
great promorphological importance, as indicating the axes in which the
growth is preponderant, and introduces other peculiar radial formations.
Regarding these axes we can generally distinguish two groups, _Artiacantha_
with a paired number (two, four, eight), and _Perissacantha_ with odd
numbers (usually three). The section of _Artiacantha_ could be divided into
three following groups:--A. Stylodiscida, with two radial spines only,
lying opposite on both poles of one equatorial axis (the "first cross
axis")--_Stylodiscus_, _Sethostylus_, _Stylocyclia_, _Xiphodictya_,
_Spongolonche_ (Pl. 31, figs. 9-12; Pl. 38, fig. 1; Pl. 42, figs. 10-12,
&c.); B. Staurodiscida, with four radial spines, lying opposite in pairs on
the poles of two crossed equatorial axes, perpendicular to one another
(first and second cross axes)--_Crucidiscus_, _Sethostaurus_,
_Staurocyclia_, _Staurodictya_, _Spongostaurus_ (Pl. 31, figs. 1-8; Pl. 37,
figs. 1-4; Pl. 42, figs. 1-6; Pl. 48, fig. 2, &c.); C. Octostylida, with
eight radial spines, opposite in pairs in four axes, which are crossed at
angles of 45°--_Heliosestrum_, _Astrosestrum_, &c. (Pl. 32, figs. 4, 5; Pl.
34, figs. 3, 6); in this latter case sometimes the radial symmetry is the
same as in many Medusæ, four larger (perradial) {408}spines alternating
with four smaller (interradial), indicating radii of first and second
order. The section of _Perissacantha_ is much smaller, and commonly
represented only by triradial forms, with three spines at equal distances
(120°)--_Triactis_, _Tripocyclia_, _Tripodictya_, _Spongotripus_, &c. (Pl.
33, fig. 6; Pl. 37, fig. 5; Pl. 42, figs. 7-9).
_Radial Arms_ on the margin of the disk appear in similar variety of
number, form, and disposition as the radial spines; but the number is here
commonly limited to from two to four, rarely five to six. The arms are
absent in the families Cenodiscida and Phacodiscida; in the four other
families they return under similar forms. These arms are direct
prolongations of the disk, and exhibit the same structure, so that they may
be regarded both as centrifugal productions of certain radii, and also
inversely as peripheral parts of a disk, the interjacent radii of which are
reduced. The regular disposition and shape of the arms, an important
character for the distinction of genera and species, is repeated in a quite
analogous manner in the four above mentioned families, so that we can
distinguish the following groups--A. Amphibrachida, with two radial arms,
opposite on the poles of one equatorial axis (the first cross
axis)--_Diplactura_, _Amphibrachium_, _Spongobrachium_ (Pl. 38, figs. 3-5;
Pl. 44, figs. 6-11); B. Triobrachida, with three radial arms; the most
important group (with all Pylodiscida); either all three arms are equal and
disposed at equal distances (_Trigonactura_, _Dictyastrum_,
_Rhopalodictyum_, Pl. 38, figs. 6-9; Pl. 43, figs. 5, 13, 16; Pl. 48, figs.
12-19), or a single odd arm differs in size and position, and is often
larger than both the opposite paired arms (_Rhopalastrum_, _Euchitonia_,
Pl. 43, figs. 6, 10, 15, &c.); C. Tetrabrachida, with four radial arms,
opposite in pairs in two crossed axes, commonly perpendicular one to
another, _Stauractura_, _Stauralastrum_, _Spongaster_, &c. (Pls. 46, 47).
The arms are commonly simple, undivided, but sometimes also forked or
branched (Pl. 43, figs. 15, 16; Pl. 47). Their basal parts are either free,
separately inserted into the margin of the circular central disk, or they
are connected by a "patagium," a peculiar connecticulum, like a
web-membrane, which is composed of a chambered, commonly more or less
spongy framework, different in texture from the lattice-work of the arms
(Pl. 38, figs. 8, 9; Pl. 43, figs. 9-16; Pl. 46). Sometimes the patagium
overgrows the whole shell. A peculiar modification of it appears in
_Stephanastrum_ (Pl. 44, fig. 1), where only the distal parts of the arms
are connected by the ring-shaped patagium, whilst the basal parts are free;
therefore open gates rest between them, like those of the Pylodiscida (Pl.
48, figs. 12-20).
The _Central Capsule_ of the #Discoidea# is constantly discoidal, more or
less lenticular; in some cases more biconvex, with vaulted faces and thin
margin; in others more medal-shaped, with flat faces and thick margin. In
the Cenodiscida alone the capsule lies freely inside the simple phacoid
shell, and is separated from it by the jelly-veil. In the other five
families the capsule encloses the central parts of the skeleton, and is
enveloped by the superficial parts of it, whilst its membrane is perforated
by radial beams {409}connecting the latter with the former. In the
Phacodiscida and Coccodiscida the capsule encloses the simple or double
medullary shell, but is itself enclosed by the cortical phacoid shell. In
all #Cyclodiscaria# (in the Porodiscida, Pylodiscida, and Spongodiscida)
the capsule fills out the greatest part of the chambered or spongy
skeleton, and is only protected by the superficial parts of it, in the
Porodiscida and Pylodiscida by the covering sieve-plates, in the
Spongodiscida by the spongy cortical substance of the shell. The growth of
the capsule corresponds to that of the including shell, gradually
increasing on the margin in the equatorial plane. Whilst in the greater
number of #Discoidea# its form continues circular, in many forms provided
with radial arms it enters into the arms and assumes their form. The
protoplasm of the capsule is commonly coloured by brown or red pigment, and
often contains many oil-globules. The nucleus is originally enclosed by the
medullary shell or the central chamber, and with increasing size enters
into the surrounding parts; in the #Cyclodiscaria# it often fills out the
internal concentric rings. The extracapsular jelly or the calymma is
commonly thick, and envelops the greater part or the whole body.
_Synopsis of the Families of the_ #Discoidea#.
-------------------------------------------------------------------------
I. Section #Phacodiscaria#.
Discoidea with external phacoid shell (or lenticular latticed cortical
shell).
-------------------------------------------------------------------------
Phacoid shell simple, without enclosed 1. CENODISCIDA.
medullary shell
Phacoid shell with { Margin without
simple or { chambered girdles, 2. PHACODISCIDA.
double {
enclosed { Margin surrounded by
medullary shell. { by chambered
{ girdles. 3. COCCODISCIDA.
-------------------------------------------------------------------------
II. Section #Cyclodiscaria#.
Discoidea without external phacoid shell (no lenticular latticed
cortical shell).
-------------------------------------------------------------------------
Surface of the { Concentric rings around
shell covered { the central chamber
by convex or { complete (without
even porous { open spaces), 4. PORODISCIDA.
sieve-plates {
(not spongy). { Concentric rings around
{ the central chamber
{ interrupted by three
{ open spaces, 5. PYLODISCIDA.
Surface of the shell spongy, not covered
by peculiar porous sieve-plates, 6. SPONGODISCIDA.
Family XVIII. #CENODISCIDA#, n. fam. (Pl. 31, fig. 11; Pl. 48, figs. 1-3).
_Definition._--#Discoidea# with simple extracapsular phacoid shell (or
lenticular latticed cortical shell), without medullary shell and without
chambered equatorial girdles.
The new family #Cenodiscida# opens the long series #Discoidea#, as their
most simple and primitive form. The circular lenticular central capsule is
enclosed by a {410}simple latticed shell of the same form, only separated
from it by a thinner or thicker jelly-veil. The lenticular or discoidal
fenestrated shell is therefore an extracapsular or "cortical shell,"
without an enclosed medullary shell.
The few genera of the Cenodiscida differ only in the shape of the
equatorial margin of the lenticular disk. In the first subfamily,
Zonodiscida, the margin is either quite simple (_Cenodiscus_) or surrounded
by a smooth, solid equatorial girdle (_Zonodiscus_). In the second
subfamily, Trochodiscida, the margin is armed with solid radial spines,
lying in the equatorial plane. According to the number and disposition of
these marginal spines, we distinguish _Stylodiscus_ (with two spines,
opposite in one equatorial axis), _Crucidiscus_ (with four spines, opposite
in pairs in two equatorial axes, perpendicular one to another),
_Theodiscus_ (with three marginal spines), and _Trochodiscus_ (with
numerous, commonly twenty to thirty, irregularly disposed spines). The
spines are constantly simple, not branched; sometimes more conical or
cylindrical, at other times more angular or pyramidal.
The two convex faces of the lenticular shell are constantly of similar
shape, commonly smooth, sometimes more or less thorny, or armed with
bristle-shaped radial spines. The pores are commonly more or less regular,
circular, and disposed in series, which are occasionally more radial, at
other times more concentric. If the wall of the hollow lens be rather
thick, the difference in the shape of the central and peripheral pores is
often striking. The central pores perforating the thick wall
perpendicularly are short cylindrical tubes; the marginal pores perforating
it in an oblique direction are longer conical tubes. The bars between the
central pores are often somewhat smaller.
_The Central Capsule_ of the Cenodiscida is in all cases a perfect,
circular, biconvex lens, the equatorial diameter of which is commonly
between two-thirds and three-fourths of the enclosing lattice-shell. The
interval between the two is filled up by the jelly-veil, or the hyaline
"calymma," which is perforated by the numerous pseudopodia that pass
through the shell-pores.
As the Cenodiscida possess the most simple shell-form of all #Discoidea#,
we may regard _Cenodiscus_ as the common ancestral form of this large
section, in the same manner as _Cenosphæra_ is the ancestral form of
#Sphæroidea#, _Cenellipsis_ of the Prunoidea, Cenolarcus of the Larcoidea.
But it is also possible that a part of Cenodiscida (or all?) arises from
the Phacodiscida by reduction and loss of the medullary shell. For in some
cases we find arising from the inside of the shell centripetal radial
beams, which end at a certain equal distance from the hollow centre (Pl.
31, fig. 11; Pl. 38, fig. 2). Cenodiscus itself can be derived either from
_Cenosphæra_ by compression of the spheroidal shell in one axis, or from
_Sethodiscus_ by loss of the intracapsular medullary shell, or from
_Actidiscus_ (the lenticular Actissa) by formation of a cortical shell
around the lenticular central capsule.
{411}_Synopsis of the Genera of the Cenodiscida._
I. Subfamily {Margin quite simple,
Zonodiscida. { without equatorial girdle, 175. _Cenodiscus_.
Margin of the disk {
without radial {Margin surrounded by a solid
spines. { siliceous equatorial girdle, 176. _Zonodiscus_.
II. Subfamily {Two spines opposite in one
Trochodiscida. { equatorial axis, 177. _Stylodiscus_.
Margin of the disk {
armed with radial {Three spines on the margin of
spines (lying in { the disk, 178. _Theodiscus_.
the equatorial {
plane). {Four spines opposite in pairs
{ in two perpendicularly
{ crossed equatorial axes, 179. _Crucidiscus_.
{
{Ten to twenty or more radial
{ spines (variable in number
{ and commonly irregular
{ in disposition), 180. _Trochodiscus_.
Subfamily 1. ZONODISCIDA, Haeckel.
_Definition._--#Cenodiscida# without radial spines on the margin of the
disk.
Genus 175. _Cenodiscus_,[214] n. gen.
_Definition._--#Cenodiscida# with simple margin of the circular disk,
without surrounding equatorial girdle and without radial spines.
The genus _Cenodiscus_ is the most simple and primitive form of all
#Discoidea#, and represents possibly the common ancestral form of this
order. The latticed shell is a simple biconvex lens, and encloses a smaller
central capsule of the same form, separated from it by the jelly-veil.
_Cenodiscus_ can be derived phylogenetically either from _Cenosphæra_ by
lenticular flattening of a simple latticed sphere, or directly from
_Actissa_ by formation of a lenticular fenestrated shell around the
lentiform central capsule. Possibly also some forms of _Cenodiscus_ can be
derived from _Sethodiscus_ by reduction and loss of the medullary shell.
1. _Cenodiscus phacoides_, n. sp. (Pl. 48, figs. 1, 1_a_).
Disk with smooth surface, without radial ribs or spines. Margin of the
lenticular biconvex disk thin, simple. Pores regular, circular; fifteen to
sixteen on the radius of the disk. (Very similar to _Sethodiscus
phacoides_, but without medullary shell.)
_Dimensions._--Diameter of the disk 0.2, of the pores 0.005.
_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.
{412}2. _Cenodiscus rotula_, n. sp.
Disk with smooth surface, without medial ribs or spines. Margin of the disk
blunt, very thick, rounded; both faces little convex. Pores regular,
circular; thirteen to fourteen on the radius of the disk. (Similar to
_Phacodiscus rotula_, Pl. 35, fig. 7, but without medullary shell.)
_Dimensions._--Diameter of the disk 0.16, of the pores 0.006.
_Habitat._--North Pacific, Station 241, depth 2300 fathoms.
3. _Cenodiscus lenticula_, n. sp.
Disk with thorny surface, scattered with small, conical spines. Margin of
the lenticular biconvex disk thin. Pores irregular, roundish; ten to eleven
on the radius of the disk.
_Dimensions._--Diameter of the disk 0.15, of the pores 0.008.
_Habitat._--South Pacific, Station 295, depth 1500 fathoms.
Genus 176. _Zonodiscus_,[215] n. gen.
_Definition._--#Cenodiscida# with surrounding solid equatorial girdle on
the margin of the lenticular disk, without radial spines.
The genus _Zonodiscus_ differs from the preceding _Cenodiscus_ only in the
development of a solid siliceous girdle around the keen margin of the
lenticular disk. This form can also be derived from _Periphæna_ or
_Perizona_ by reduction and loss of the medullary shell. The same girdle
formation returns not only in both these Phacodiscida (Pl. 32, fig. 7; Pl.
33, fig. 4), but also in the Porodiscid _Perichlamydium_.
1. _Zonodiscus saturnalis_, n. sp.
Disk with smooth surface, without radial spines. Pores regular, circular,
fifteen to sixteen on the radius of the disk, in its distal half arranged
in fifty to sixty radial series, which are separated by prominent radial
crests or ribs. The crests are prolonged into the proximal half of the thin
solid equatorial girdle, which is one-third as broad as the radius of the
disk.
_Dimensions._--Diameter of the disk 0.25, of the pores 0.05.
_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.
Subfamily 2. TROCHODISCIDA, Haeckel.
_Definition._--#Cenodiscida# with radial spines on the margin of the disk,
disposed in the equatorial plane.
Genus 177. _Stylodiscus_,[216] n. gen.
_Definition._--#Cenodiscida# with two radial spines on the margin of the
disk, opposite in one equatorial axis.
{413}The genus _Stylodiscus_ opens the series of the Trochodiscida or of
those Cenodiscida in which the thin margin of the hollow lenticular disk is
armed with a number of solid radial spines, situated in its equatorial
plane. _Stylodiscus_ is at the same time the most simple form of the
Stylodiscida, or of the numerous #Discoidea# (belonging to different
families) in which the disk bears only two spines, opposite in one
equatorial axis. Hitherto only two species of this genus have been
observed, but they seem to represent two different subgenera.
Subgenus 1. _Stylentodiscus_, Haeckel.
_Definition._--Internal cavity of the shell with centripetal axial rods.
1. _Stylodiscus endostylus_, n. sp. (Pl. 31, fig. 11).
_Sethostylus endostylus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxi,
fig. 11).
Disk with smooth surface and dentated margin. Pores irregular, roundish;
ten to twelve on the radius of the disk. Marginal teeth conical, short,
irregular. Both opposite polar spines cylindrical, longer than the diameter
of the disk, and as broad as one larger pore. On the inside of the hollow
disk both spines are prolonged into two strong centripetal axial rods,
which do not reach the centre. Also a number of smaller centripetal axial
rods surrounds the central cavity, so that an original medullary shell
(_Sethostylus_) seems to have been lost (comp. above, p. 410).
_Dimensions._--Diameter of the disk 0.25, of the pores 0.005 to 0.02;
length of the polar spines 0.3 and more, thickness 0.012.
_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.
Subgenus 2. _Stylexodiscus_, Haeckel.
_Definition._--Internal cavity of the shell without axial rods.
2. _Stylodiscus amphistylus_, n. sp.
Disk with smooth surface and smooth margin. Pores regular, circular; eight
to nine on the radius of the disk. Both opposite polar spines pyramidal,
sulcated, about as long as the radius of the disk, and three times as long
as broad at the base. Inner cavity of the disk simple, without centripetal
rods.
_Dimensions._--Diameter of the disk 0.15, of the pores 0.007; length of the
polar spines 0.08, basal breadth 0.03.
_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.
{414}Genus 178. _Theodiscus_,[217] n. gen.
_Definition._--#Cenodiscida# with three radial spines on the margin of the
disk, placed in its equatorial plane.
The genus _Theodiscus_ is the most simple form of those very numerous
#Discoidea# in which three rays are developed on the margin of the disk; a
symbol of the Christian dogma of the Trinity. Commonly the three angles
between the three spines are equal, more rarely one angle is larger than
the two others which are equal. The shell of some species is nearly
spherical (formerly separated by me as _Theosphæra_), whilst in others it
is a flattened biconvex lens.
Subgenus 1. _Theodiscoma_, Haeckel.
_Definition._--Angles between the three radial spines equal (triangle
equilateral).
1. _Theodiscus divinus_, n. sp.
Disk nearly spherical, with smooth surface. Pores regular, circular,
hexagonally framed; seven to eight on the radius. Three angles between the
spines equal. Spines prismatic, straight, twice as broad as one pore, eight
to eleven times as long as the shell diameter.
_Dimensions._--Diameter of the disk 0.1, of the pores 0.006; length of the
spines 0.8 to 1.1, breadth 0.01.
_Habitat._--Central Pacific, Station 265, surface.
2. _Theodiscus christianus_, n. sp.
Disk nearly spherical, with smooth surface. Pores regular, circular,
prolonged into short cylindrical, prominent tubuli, half as high as broad;
eight to nine on the radius. Three angles between the spines equal. Spines
prismatic, straight, twice as broad as one pore, twelve to fifteen times as
long as the shell diameter.
_Dimensions._--Diameter of the disk 0.08, of the pores 0.005; length of the
spines 1.1 to 1.2, breadth 0.01.
_Habitat._--Central Pacific, Station 271, surface.
3. _Theodiscus trinitatis_, n. sp.
Disk a rather flattened, biconvex lens, about twice as broad as thick.
Pores regular, circular, not prolonged into tubuli; five to six on the
radius. Three angles between the spines equal. Spines pyramidal, three
times as broad as one pore, about twice as long as the shell diameter.
{415}_Dimensions._--Diameter of the disk 0.06, of the pores 0.007; length
of the spine 0.12, basal breadth 0.02.
_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.
Subgenus 2. _Theodiscura_, Haeckel.
_Definition._--Angles between the three radial spines unequal, two paired
angles equal, larger or smaller than the odd angle (triangle isosceles).
4. _Theodiscus vanitatis_, n. sp.
Disk nearly spherical, with smooth surface. Pores irregular, roundish;
eight to ten on the radius. Three angles between the spines unequal; one
odd angle larger than both others. Spines pyramidal, of unequal size; one
odd spine larger, both others smaller than the shell diameter.
_Dimensions._--Diameter of the disk 0.12, pores 0.004 to 0.006; length of
the odd spine 0.2, of the paired spines 0.1.
_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.
5. _Theodiscus nirvana_, n. sp.
Disk a flat biconvex lens, about twice as broad as thick. Pores regular,
circular; ten to twelve on the radius. Three angles between the spines
unequal; one odd angle smaller than both others. Spines prismatic, very
long and thin, twice as broad as one pore, ten to twelve times as long as
the shell diameter.
_Dimensions._--Diameter of the disk 0.1, pores 0.005; length of the spines
1 to 1.2 or more, breadth 0.01.
_Habitat._--Indian Ocean, Ceylon, surface, Haeckel.
Genus 179. _Crucidiscus_,[218] n. gen.
_Definition._--#Cenodiscida# with four radial spines on the margin of the
disk, crossed in the equatorial plane.
The genus _Crucidiscus_ is the most simple form of the Staurodiscida, or of
the numerous #Discoidea# (belonging to different families) in which the
margin of the disk bears four radial spines, lying in the equatorial plane,
and crossed at right angles. Whilst commonly the internal shell-cavity of
_Crucidiscus_ is quite simple, in one case it bears four centripetal axial
rods, as inner prolongations of the outer radial cross-spines, perhaps
indications of a lost medullary shell (comp. p. 410).
{416}Subgenus 1. _Staurentodiscus_, Haeckel.
_Definition._--Internal cavity of the shell with centripetal axial rods.
1. _Crucidiscus endostaurus_, n. sp. (Pl. 48, fig. 2).
Disk with smooth surface and smooth simple margin. Pores regular, circular;
thirteen to fourteen on the radius of the disk. Four crossed spines
conical, strong, longer than the radius of the disk, on the inside
prolonged into four thinner centripetal axial rods, which do not reach the
centre. In the middle part of the disk also some other short axial rods
arise from the inside, not reaching the centre (as in _Stylodiscus
endostylus_, Pl. 31, fig. 11).
_Dimensions._--Diameter of the disk 0.16, of the pores 0.004; length of the
spines 0.2, breadth 0.014.
_Habitat._--North Pacific, Station 253, depth 3125 fathoms.
Subgenus 2. _Staurexodiscus_, Haeckel.
_Definition._--Internal cavity of the shell without centripetal axial rods.
2. _Crucidiscus cuspidatus_, n. sp.
Disk with smooth surface and simple smooth margin. Pores regular, circular;
seven to eight on the radius of the disk. Four crossed spines pyramidal,
with prominent edges, somewhat shorter than the radius of the disk, twice
as broad at their thick base as one pore. No internal axial rods in the
shell cavity.
_Dimensions._--Diameter of the disk 0.12, of the pores 0.005; length of the
spines 0.05, basal breadth 0.025.
_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.
3. _Crucidiscus echinatus_, n. sp.
Disk with thorny surface and thorny margin. Pores regular, circular, six to
seven on the radius. Four crossed spines pyramidal (four sided?), about as
long as the radius of the disk, as broad at their base as one pore. No
internal axial rods. Spines of the surface short, conical.
_Dimensions._--Diameter of the disk 0.14, of the pores 0.008; length of the
spines 0.08, basal breadth 0.02.
_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.
4. _Crucidiscus cruciatus_, n. sp.
Disk with smooth surface and broad dentated margin. Pores regular,
circular; eleven to twelve on the radius. Four crossed spines pyramidal,
sulcated, about as long as the radius of the disk, as {417}broad at their
base as the radiated margin, which bears fifty to sixty triangular pointed
teeth of irregular size. (Similar to _Sethostaurus cruciatus_, Pl. 31, fig.
5, but without internal axial rods and medullary shell.)
_Dimensions._--Diameter of the disk 0.2, of the pores 0.007; length of the
spines 0.1, basal breadth 0.02.
_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.
Genus 180. _Trochodiscus_,[219] n. gen.
_Definition._--#Cenodiscida# with numerous (ten to twenty or more) radial
spines on the margin of the disk, situated in its equatorial plane.
The genus _Trochodiscus_ bears on the thin margin of the latticed disk a
variable number of radial spines (commonly ten to twenty, sometimes fifty
to eighty or more). Their size and disposition are commonly more or less
irregular. For the most part all the marginal spines lie in the equatorial
plane; but sometimes part of them are crowded into two or four parallel
girdles. Several species of this genus are very similar to some species of
_Heliodiscus_, and only differ in the absence of the medullary shell,
perhaps in consequence of the phylogenetic loss of it; if this be the case,
the former are to be derived from the latter (compare p. 410).
Subgenus 1. _Trochodisculus_, Haeckel.
_Definition._--Bases of the marginal spines free, not connected by a solid
equatorial girdle.
1. _Trochodiscus cenophacus_, n. sp.
Disk with smooth surface. Pores regular, circular; eleven to twelve on the
radius. Marginal spines sixteen to twenty, conical, of irregular size and
disposition, about three times as long as broad, and as long as the radius
of the disk.
_Dimensions._--Diameter of the disk 0.15, of the pores 0.006; length of the
spines 0.06 to 0.09, basal breadth 0.02 to 0.03.
_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.
2. _Trochodiscus medusinus_, n. sp.
Disk with smooth surface. Pores regular, circular; nine to ten on the
radius. Marginal spines ten to twelve, equilateral triangular, deeply
sulcated, about half as long and broad as the radius of the disk. (Very
similar to _Heliosestrum medusinum_, Pl. 34, fig. 6, but without enclosed
medullary shell. Compare p. 410.)
_Dimensions._--Diameter of the disk 0.2, of the pores 0.01; length of the
spines 0.05, basal breadth 0.05.
_Habitat._--North Pacific, Station 241, depth 2300 fathoms.
{418}3. _Trochodiscus odontotrochus_, n. sp.
Disk with smooth surface, in the distal part radially sulcated. Pores
irregular, roundish; twelve to fourteen on the radius. Marginal spines very
short and numerous (thirty to forty), conical, scarcely one-fourth as long
as the radius of the disk, which resembles a wheel with marginal teeth.
_Dimensions._--Diameter of the disk 0.18, of the pores 0.004; length of the
spines 0.02, basal breadth 0.01.
_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.
4. _Trochodiscus solaris_, n. sp.
Disk with smooth surface. Pores subregular, circular; eight to nine on the
radius. Marginal spines very numerous (sixty to eighty), in two to four
girdles densely crowded together, the largest as long as the diameter of
the disk, bent and conical. (Similar to _Heliodiscus solaster_, Pl. 34,
fig. 4, but without medullary shell.)
_Dimensions._--Diameter of the disk 0.15, of the pores 0.008; length of the
spines 0.05 to 0.15, basal breadth 0.01.
_Habitat._--South Pacific, Station 300, depth 1375 fathoms.
5. _Trochodiscus echiniscus_, n. sp.
Disk with spiny surface. Pores irregular, roundish; ten to eleven on the
radius. Marginal spines conical, very numerous (forty to fifty), irregular
in size and disposition, the largest half as long as the radius of the
disk. (Similar to _Heliodiscus echiniscus_, Pl. 34, fig. 5, but without
medullary shell.)
_Dimensions._--Diameter of the disk 0.18, of the pores 0.005 to 0.015;
length of the spines 0.02 to 0.04, basal breadth 0.01.
_Habitat._--North Atlantic, Færöe Channel, John Murray.
Subgenus 2. _Pristodiscus_, Haeckel.
_Definition._--Bases of the marginal spines connected by a solid siliceous
equatorial girdle.
6. _Trochodiscus stellaris_, n. sp. (Pl. 48, fig. 3).
Disk with smooth surface. Pores subregular, circular; seven to eight on the
radius. Marginal spines twelve to sixteen, triangular, of subregular size
and disposition, about half as long as the radius of the disk, connected at
their broad base by a solid equatorial girdle of half the breadth; girdle
and spines radially striped.
_Dimensions._--Diameter of the disk 0.25, of the pores 0.015; length of the
spines 0.04 to 0.06, basal breadth 0.02 to 0.04.
_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.
{419}7. _Trochodiscus cingillum_, n. sp.
Disk with smooth surface, in the distal part radially sulcated. Pores
regular, circular; twelve to thirteen on the radius. Marginal spines twenty
to twenty-four, triangular, of equal size and at regular distances, only
one-fourth as long as the radius of the disk, connected at their broad base
by a solid equatorial girdle of the double breadth. (Similar to
_Heliodiscus cingillum_, Pl. 33, fig. 7, but without medullary shell.)
_Dimensions._--Diameter of the disk 0.22, of the pores 0.004; length of the
spines 0.02, basal breadth 0.02
_Habitat._--South Pacific, Station 285, depth 2375 fathoms.
Family XIX. #PHACODISCIDA#, Haeckel (Pls. 31-35).
_Phacodiscida_, Haeckel, 1881, Prodromus, p. 456.
_Definition._--#Discoidea# with simple extracapsular phacoid shell (or
lenticular latticed cortical shell), connected by radial beams with an
intracapsular, simple or double, concentric medullary shell, without
chambered equatorial girdles.
The family #Phacodiscida# comprises a large number of splendid forms (about
a hundred species), which agree with the preceding Cenodiscida in the
possession of the characteristic extracapsular "phacoid shell," but differ
from them in having one or two intracapsular "medullary shells"; these
concentric spherical medullary shells are connected with the lenticular
cortical shell or phacoid shell by means of radial beams perforating the
central capsule. The Phacodiscida bear therefore the same relation to the
Cenodiscida that the Disphærida and Trisphærida do to the Monosphærida.
Formerly several species belonging to the family were described by
Ehrenberg and Johannes Müller, but not distinguished from the Sphæroidea,
genus _Haliomma_ (_e.g._, _Haliomma sol_ et _Haliomma humboldtii_ of the
former, _Haliomma amphidiscus_ of the latter). For these oldest known
species I constituted in 1862 my genus _Heliodiscus_ (Monogr. d. Radiol.,
p. 436). Some other genera were afterwards (1875) figured by Ehrenberg as
_Periphæna_ and _Chilomma_. The rich material of the Challenger revealed
this family as very polymorphic and widely distributed, so that in my
Prodromus (1881, p. 457) I could enumerate eighteen different genera of
Phacodiscida. This number is here reduced to fifteen, uniting several of
them into one genus as "subgenera."
_The Medullary Shell_ of the Phacodiscida, or the intracapsular latticed
shell, is either simple and spherical, or double, composed of two
concentric spheres, which are united by a variable number of radial beams.
We could distinguish therefore as two subfamilies the Carpodiscida (with
simple medullary shell) and the Thecodiscida (with double concentric
medullary shell); the former corresponding to the Carposphærida (or
_Dyosphæria_), the latter to the Thecosphærida (or _Triosphæria_). But as
this difference seems not to be so important as the different shape of the
disk margin, we prefer this latter as a character {420}for the separation
of subfamilies. The form of the medullary shells is commonly quite
spherical (as also in the above mentioned #Sphæroidea#); sometimes it is a
little compressed in the same direction as the enclosing lenticular phacoid
shell. The diameter of the latter is commonly three to four times as large
as the diameter of the medullary shell; if this be double (in the
Thecodiscida) then the diameter of the outer medullary shell is commonly
three to four times as large as that of the inner. The radial beams
connecting the two seem to be very variable in number and disposition
(compare Pl. 31, fig. 8; Pl. 32, figs. 3, 4_a_, 7, 8_a_; Pl. 33, figs. 2,
3; Pl. 35, figs. 4, 8, 9, &c.).
_The Radial Beams_, which connect the medullary shell with the cortical or
"phacoid shell," and which pierce the membrane of the lenticular central
capsule, are commonly aggregated into two polar bunches around the
shortened axis of the disk (compare Pl. 31, fig. 8; Pl. 32, figs. 3, 8; Pl.
33, figs. 2, 3, &c.). Their number seems to be usually between ten and
thirty. More rarely piercing radial beams lie also in the equatorial plane,
and then commonly as inner prolongations of the outer marginal spines; so
we find two opposite in one axis, in _Heliostylus_ (Pl. 34, figs. 1, 2), or
four opposite in pairs in two crossed axes, in _Phacostaurus_ (Pl. 31,
figs. 1, 2, 7). Often the thickness of the beams increases from the centre
towards the periphery.
_The Phacoid Shell_, or the lenticular extracapsular cortical shell,
exhibits in the Phacodiscida quite the same general character as in the
Cenodiscida, above described (p. 410). Commonly the equatorial diameter of
the lens is twice to three times as large as the vertical diameter or the
shortened "main axis." The convexity of both opposite faces is either quite
even to the sharp margin (Pl. 31, fig. 2; Pl. 33, figs. 2, 5), or the
central part of the lens is more strongly vaulted, and often the margin is
thickened or truncated (Pl. 31, fig. 10; Pl. 35, fig. 7). The surface of
the lens is commonly smooth, but sometimes also covered with bristle-shaped
radial spines (Pl. 34, figs. 3, 5; Pl. 32, figs. 2, 3); rarely these spines
are prolonged and branched (Pl. 35, figs. 3, 5). The pores of the phacoid
shell are usually quite regular, circular, and regularly arranged, either
in more concentric or in more radial rows; the latter are sometimes
separated by radial crests arising towards the margin (Pl. 35, fig. 6). If
the wall of the phacoid shell be much thickened, the pores in its central
part are shorter and cylindrical, in its marginal part longer and conical
(Pl. 31, fig. 7; Pl. 32, fig. 1).
_The Margin of the Lens_ of the Phacodiscida is very polymorphic, and
serves mainly for the separation of genera. In the first subfamily,
Sethodiscida, it is either quite simple (Pl. 35, figs. 6-8) or surrounded
by a thin solid equatorial girdle, the basal part of which is often
radially striped (Pl. 32, figs. 7, 8). In the second subfamily,
Heliosestrida, we find on the margin a small number of radial spines in the
equatorial plane regularly disposed, either two opposite in one axis (Pl.
31, figs. 9-12) or four opposite in pairs in two crossed axes (Pl. 31,
figs. 1-8), or eight opposite in pairs in four axes, crossed at angles of
45° (Pl. 34, figs. 3, 6); in the latter case we can sometimes distinguish
{421}(as in many Medusæ) four larger perradial spines alternating with four
smaller interradial spines. Often in one and the same species occur
abnormalities in number and disposition of the radial spines, three or five
spines instead of four, or also seven or nine spines instead of eight;
often both halves of the disk become asymmetrical. If the number of the
marginal spines exceed eight to ten, they commonly become very variable in
size and irregular in disposition; these variations characterise the third
subfamily, Heliodiscida. Commonly also here all spines lie in the
equatorial plane; but sometimes they become crowded in several parallel
circles on both sides of the margin (Pl. 32, fig. 1). The form of the
marginal spines is commonly conical or flattened triangular, often also
pyramidal or deeply furrowed (Pl. 31, figs. 6-9). Very rarely the spines
are fenestrated (Pl. 35, fig. 1); only in one genus (_Heliodrymus_) they
are all or partly branched (Pl. 33, fig. 9; Pl. 35, figs. 3, 5).
The peculiar development of the phacoid shell has been already described by
J. Müller (compare my Monograph, 1862, pp. 156, 438).
_The Central Capsule_ of the Phacodiscida is everywhere circular,
lenticular, envelops the medullary shell, and is enclosed by the phacoid
shell, perforated by the radial beams, which connect the latter to the
former.
_Synopsis of the Genera of the Phacodiscida._
-------------------------------------------------------------------------
I. Subfamily Sethodiscida.
Margin of the disk without radial spines.
-------------------------------------------------------------------------
Margin simple, without {Medullary shell simple, 181. _Sethodiscus_.
equatorial girdle. {
{Medullary shell double, 182. _Phacodiscus_.
Margin surrounded by a {Medullary shell simple, 183. _Periphæna_.
hyaline equatorial girdle. {
{Medullary shell double, 184. _Perizona_.
-------------------------------------------------------------------------
II. Subfamily Heliosestrida.
Margin of the disk with two to eight solid radial spines, usually
quite regularly disposed. (Number usually constant.)
-------------------------------------------------------------------------
Two radial spines {Medullary shell simple, 185. _Sethostylus_.
(opposite in one axis). {
{Medullary shell double, 186. _Phacostylus_.
Three radial spines. Medullary shell simple, 187. _Triactiscus_.
Four radial spines (in {Medullary shell simple, 188. _Sethostaurus_.
cross form). {
{Medullary shell double, 189. _Phacostaurus_.
Six radial spines. Medullary shell simple, 190. _Distriactis_.
Eight radial spines. {Medullary shell simple, 191. _Heliosestrum_.
{
{Medullary shell double, 192. _Astrosestrum_.
-------------------------------------------------------------------------
III. Subfamily Heliodiscida.
Margin of the disk with numerous (ten to twenty or more) radial
spines, usually irregularly disposed. (Number variable.)
-------------------------------------------------------------------------
Radial spines all simple, {Medullary shell simple, 193. _Heliodiscus_.
not branched. {
{Medullary shell double, 194. _Astrophacus_.
Radial spines all or }Medullary shell simple, 195. _Heliodrymus_.
partly branched. }
{422}Subfamily 1. SETHODISCIDA, Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# without radial spines on the margin of the
disk.
Genus 181. _Sethodiscus_,[220] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with simple medullary shell and simple margin
of the circular disk, without surrounding equatorial girdle and without
radial spines.
The genus _Sethodiscus_ is the most simple and primitive form of all
Phacodiscida, and may be regarded as the common ancestral form of this
family. The simple spherical medullary shell is connected by a variable
number of radial beams with the lenticular or discoidal cortical shell (or
"phacoid shell"). The margin of this latter is quite simple, circular,
without solid equatorial girdle or radial spines. From the nearly allied
genus _Carposphæra_ of the #Sphæroidea#, its probable ancestral form,
_Sethodiscus_ can be derived simply by lenticular compression of the
spheroidal cortical shell.
Subgenus 1. _Sethodiscinus_, Haeckel.
_Definition._--Surface of the disk smooth, without radial ribs or spines.
1. _Sethodiscus phacoides_, n. sp.
Disk with smooth surface, three times as broad as the medullary shell.
Pores regular, circular; fourteen to fifteen on the radius of the disk.
(Very similar to _Periphæna cincta_, Pl. 33, fig. 4, but without the girdle
of the margin.)
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.07, of
the pores 0.005.
_Habitat._--Pacific, central area, Stations 270 to 274, in various depths.
2. _Sethodiscus macroporus_, n. sp.
Disk with smooth surface, twice as broad as the medullary shell. Pores
regular, circular, very large; five to six on the radius of the disk.
(Remarkable for the extraordinary size of the pores, which reaches half the
radius of the medullary shell.)
_Dimensions._--Diameter of the disk 0.1, of the medullary shell 0.05, of
the pores 0.012.
_Habitat._--North Atlantic, Gulf Stream, Færöe Channel, John Murray.
3. _Sethodiscus microporus_, n. sp.
Disk with smooth surface, four times as broad as the medullary shell. Pores
regular, circular, very small; twenty-two to twenty-four on the radius of
the disk. (The small pores are scarcely half as broad as the thick bars
between them.)
{423}_Dimensions._--Diameter of the disk 0.25, of the medullary shell 0.06,
of the pores 0.002.
_Habitat._--South Pacific, Station 288, surface.
4. _Sethodiscus lenticula_, n. sp. (Pl. 33, figs. 1, 2).
Disk with smooth surface, four times as broad as the medullary shell. Pores
irregular, polygonal; eight to nine on the radius of the disk. (The pores
of the medullary shell, fig. 2, are also irregular, polygonal, or
roundish.)
_Dimensions._--Diameter of the disk 0.17, of the medullary shell 0.04, of
the pores 0.01.
_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.
5. _Sethodiscus macrococcus_, n. sp. (Pl. 33, fig. 3).
Disk with smooth surface, two and a half times as broad as the medullary
shell. Pores irregular, polygonal; eleven to twelve on the radius of the
disk. (The pores of the medullary shell, fig. 3, are regular, circular,
with elevated hexagonal frames between them. The figured specimen is a
young one, both halves of the biconvex disk being not yet united in the
equatorial plane.)
_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.065, of
the pores 0.01.
_Habitat._--North Pacific, Station 244, depth 2900 fathoms.
6. _Sethodiscus micrococcus_, n. sp.
Disk with smooth surface, five times as broad as the medullary shell. Pores
irregular, roundish, very small; twenty-six to twenty-eight on the radius
of the disk. (The pores of the small medullary shell are regularly
circular, of the same size as those of the disk.)
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.04, of
the pores 0.002.
_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.
Subgenus 2. _Sethodisculus_, Haeckel.
_Definition._--Surface of the disk with elevated radial ribs or spines.
7. _Sethodiscus radiatus_, Haeckel.
_Haliomma radians_, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 50.
_Haliomma radiatum_, Ehrenberg, 1854, Mikrogeol., Taf. xxi. fig. 54.
Disk with radiated surface, four times as broad as the medullary shell.
Pores regularly circular; nine to ten on the radius of the disk, arranged
in radial series (about forty), which are separated by smooth crests, not
prominent on the smooth margin.
_Dimensions._--Diameter of the disk 0.12, of the medullary shell 0.03, of
the pores 0.003.
_Habitat._--Fossil in Tertiary deposits of the Mediterranean, Greece,
Sicily, Oran, &c.
{424}8. _Sethodiscus echinatus_, Haeckel.
_Haliomma echinatum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 74, Taf. xxvii. fig. 2.
Disk with radiated thorny surface, three times as broad as the medullary
shell. Pores regular, circular; eleven to twelve on the radius of the disk,
arranged in radial series (about sixty), which are separated by thorny
crests, prominent a little on the dentated margin.
_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.06, of
the pores 0.01.
_Habitat._--Fossil in the rocks of Barbados.
9. _Sethodiscus cristatus_, n. sp.
Disk with radiated surface, four times as broad as the medullary shell.
Pores regularly circular; sixteen to seventeen on the radius of the disk,
arranged in radial series (about eighty), which are separated in the distal
half by smooth elevated crests, strongly prominent on the dentated margin.
(Very similar to _Phacodiscus cristatus_, Pl. 35, fig. 6, but with simple
medullary shell.)
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05, of
the pores 0.005.
_Habitat._--South Pacific, Station 285, depth 2375 fathoms.
Genus 182. _Phacodiscus_,[221] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with double medullary shell and simple margin
of the circular disk, without surrounding equatorial girdle and without
radial spines.
The genus _Phacodiscus_ differs from the ancestral genus _Sethodiscus_ only
in the duplication of the medullary shell, and has therefore the same
relation to it that _Thecosphæra_ in the #Sphæroidea# exhibits to
_Carposphæra_. Both former discoidal genera differ from the two latter
spheroidal by the lenticular flattening of the cortical shell.
Subgenus 1. _Phacodiscinus_, Haeckel.
_Definition._--Surface of the disk smooth, without radial ribs or spines.
1. _Phacodiscus rotula_, n. sp. (Pl. 35, fig. 7).
Disk with smooth surface, four and a half times as broad as the outer and
fourteen times as broad as the inner medullary shell. Pores regularly
circular; sixteen to eighteen on the radius of the disk. Margin of the lens
very thick, truncated, nearly as broad as the outer medullary shell.
_Dimensions._--Diameter of the disk 0.21, of the outer medullary shell
0.045, of the inner 0.015; pores 0.008.
_Habitat._--North Pacific, Station 224, depth 1850 fathoms.
{425}2. _Phacodiscus lentiformis_, n. sp. (Pl. 35, fig. 8).
Disk with smooth surface, three and a half times as broad as the outer, and
ten times as broad as the inner medullary shell. Pores regularly circular;
twelve to thirteen on the radius of the disk. Margin of the disk sharp, as
in a biconvex lens.
_Dimensions._--Diameter of the disk 0.25, of the outer medullary shell
0.07, of the inner 0.025; pores 0.01.
_Habitat._--Central Pacific, Station 265, depth 2900 fathoms; fossil in
Barbados.
3. _Phacodiscus grandis_, n. sp.
Disk with thorny surface, five times as broad as the outer, and fifteen
times as broad as the inner medullary shell. Pores regularly circular;
twenty-two to twenty-four on the radius of the disk. Margin of the disk
thick, rounded.
_Dimensions._--Diameter of the disk 0.45, of the outer medullary shell
0.09, of the inner 0.03; pores 0.01.
_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.
Subgenus 2. _Phacodisculus_, Haeckel.
_Definition._--Surface of the disk with elevated radial ribs or spines.
4. _Phacodiscus echiniscus_, n. sp.
Disk with spiny surface, four times as broad as the outer, and ten times as
broad as the inner medullary shell. Pores irregularly roundish; fourteen to
fifteen on the radius of the disk. Margin of the disk sharp, as in a
biconvex lens.
_Dimensions._--Diameter of the disk 0.3, of the outer medullary shell 0.75,
of the inner 0.03; pores 0.007.
_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.
5. _Phacodiscus clypeus_, n. sp. (Pl. 35, figs. 6, 9).
Disk with radiated surface, four times as broad as the outer, and twelve
times as broad as the inner medullary shell. Pores regularly circular;
sixteen to eighteen on the radius of the disk; in the distal half disposed
in sixty to seventy radial series, which are separated by prominent crests;
the sharp margin therefore a little jagged.
_Dimensions._--Diameter of the disk 0.2, of the outer medullary shell 0.05,
of the inner 0.017; pores 0.006.
_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.
{426}Genus 183. _Periphæna_,[222] Ehrenberg, 1873 Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, p. 246.
_Definition._--#Phacodiscida# with simple medullary shell, without radial
spines, but with a solid equatorial girdle around the margin of the
lenticular disk.
The genus _Periphæna_, founded by Ehrenberg in 1873 for the fossil
_Periphæna decora_ of Barbados, differs from its ancestral form
_Sethodiscus_ in the development of a very thin siliceous solid girdle
around the margin of the lenticular disk; this girdle lies in the
equatorial plane of the shell, and reappears in similar form in
_Perichlamydium_ among the Porodiscida, in _Spongophacus_ among the
Spongodiscida, and in _Zonodiscus_ among the Cenodiscida.
1. _Periphæna cincta_, n. sp. (Pl. 33, fig. 4).
Disk with smooth surface, four times as broad as the medullary shell. Pores
regularly circular; fourteen to sixteen on the radius of the disk. Girdle
of the margin about half as broad as the radius of the medullary shell, in
the distal half structureless, in the proximal half with seventy to eighty
short radial ribs.
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05, of
the pores 0.005.
_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.
2. _Periphæna decora_, Ehrenberg.
_Periphæna decora_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 80, Taf. xxviii. fig. 6.
Disk with smooth surface, three times as broad as the medullary shell.
Pores regular, circular; twenty to twenty-two on the radius of the disk,
disposed in radial series. Girdle of the margin nearly as broad as the
radius of the medullary shell, in the distal half structureless, in the
proximal half with eighty to ninety short radial ribs.
_Dimensions._--Diameter of the disk 0.25, of the medullary shell 0.08, of
the pores 0.06.
_Habitat._--Fossil in Barbados.
3. _Periphæna statoblastus_, n. sp.
Disk with smooth surface, five times as broad as the medullary shell. Pores
regularly circular; twenty-four to twenty-six on the radius of the disk,
disposed in radial series, those in the distal half of the disk being
separated by piercing radial beams. Girdle of the margin twice as broad as
the radius of the medullary shell, in the whole breadth with one hundred
and twenty to one hundred and thirty piercing radial ribs, the
prolongations of the beams.
_Dimensions._--Diameter of the disk 0.3, of the medullary shell 0.06, of
the pores 0.04.
_Habitat._--South Pacific, Station 300, depth 1375 fathoms.
{427}Genus 184. _Perizona_,[223] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with double medullary shell, without radial
spines, but with a solid equatorial girdle around the margin of the
lenticular disk.
The genus _Perizona_ differs from its ancestral form _Phacodiscus_ in the
development of a thin solid siliceous girdle, lying in the equatorial
plane around the margin of the disk. The two genera bear the same relation
to each other that _Periphæna_ bears to _Sethodiscus_. But in the two
latter genera the spherical medullary shell is simple, in the two former
double.
1. _Perizona scutella_, n. sp. (Pl. 32, fig. 7).
Disk with smooth surface, in the distal third radiated, four times as broad
as the outer, and ten times is broad as the inner medullary shell. Pores
subregular, circular; thirteen to fourteen on the radius of the disk, in
the marginal part separated by eighty to ninety prominent radial crests,
which are prolonged into the proximal half of the solid girdle. Breadth of
the girdle equal to that of the inner medullary shell.
_Dimensions._--Diameter of the disk 0.25, of the outer medullary shell
0.06, of the inner 0.025; pores 0.007.
_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.
2. _Perizona pterygota_, n. sp. (Pl. 32, figs. 8, 8_a_).
Disk with smooth surface, six times as broad as the outer, and fifteen
times as broad as the inner medullary shell. Pores regularly circular;
eighteen to twenty on the radius of the disk. Margin much thickened and
truncated, abruptly separated in the equatorial circumference from the
peripheral sharp margin of the solid girdle; breadth of the girdle equal to
that of the outer medullary shell.
_Dimensions._--Diameter of the disk 0.25, of the outer medullary shell
0.04, of the inner 0.015; pores 0.006.
_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.
Subfamily 2. HELIOSESTRIDA, Haeckel.
_Definition._--#Phacodiscida# with a constant number of radial spines on
the margin of the disk (two, three, four, six, or eight), which are
commonly regularly disposed (sometimes more or less irregularly).
{428}Genus 185. _Sethostylus_,[224] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with simple medullary shell and with two
radial spines on the margin of the disk, opposite in the equatorial axis.
The genus _Sethostylus_ opens the series of the Heliosestrida or of those
Phacodiscida in which a constant number of radial spines (two to eight) is
more or less regularly disposed on the margin of the disk. All these
marginal spines lie in the equatorial plane of the lens, and have in the
same species a rather constant number and similar size, a certain form and
disposition. Sometimes they incline more or less to irregular variations.
In _Sethostylus_ there are only two spines, opposite in the equatorial
diameter of the lens; it corresponds to _Stylocyclia_ among the
Coccodiscida, and to _Xiphodictya_ among the Porodiscida.
Subgenus 1. _Sethostylium_, Haeckel.
_Definition._--Margin of the disk simple, smooth, without equatorial girdle
and without a corona of marginal spines.
1. _Sethostylus distyliscus_, n. sp. (Pl. 31, fig. 9).
Disk with smooth surface, three times as broad as the medullary shell.
Pores regular, circular; nine to ten on the radius of the disk, in the
outer rows cylindrical. Margin of the disk simple, smooth, thin, without
peculiar equatorial girdle, radially striped by the prominent beams of the
peripheral series of pores. Both marginal spines of equal size, pyramidal,
sulcated, about as long as the radius of the disk and as broad at the base
as the medullary shell.
_Dimensions._--Diameter of the disk 0.13 to 0.16, of the medullary shell
0.04 to 0.05; length of both opposite spines 0.06 to 0.08, basal breadth
0.03 to 0.04.
_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.
2. _Sethostylus dicylindrus_, n. sp. (Pl. 31, fig. 10).
Disk with smooth surface, four times as broad as the medullary shell. Pores
regular, circular; sixteen to eighteen on the radius of the disk. Margin of
the disk simple, smooth, thick, without peculiar equatorial girdle. Both
marginal spines cylindrical, about as long as the diameter of the disk,
about twice as broad as a single pore. (Walls of the disk in the central
part twice to three times as thick as in the peripheral part.)
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05;
length of both spines 0.2 to 0.3, breadth 0.008.
_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.
{429}Subgenus 2. _Heliostylus_, Haeckel, 1881, Prodromus, p. 457.
_Definition._--Margin of the disk with a solid equatorial girdle or a
corona of radial spines.
3. _Sethostylus dentatus_, n. sp. (Pl. 34, fig. 1).
_Heliostylus dentatus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxiv.
fig. 1).
Disk with smooth surface, six times as broad as the medullary shell. Pores
regular, circular; eighteen to twenty on the radius of the disk. Margin of
the disk with a broad solid equatorial girdle, which bears fifty to sixty
strong conical teeth on the periphery; teeth about as long as the diameter
of the medullary shell. Both opposite marginal spines cylindro-conical,
about as long as the diameter of the disk, and as broad as the girdle.
_Dimensions._--Diameter of the disk 0.3, of the medullary shell 0.05;
length of both main spines 0.2 to 0.3, breadth 0.02.
_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.
4. _Sethostylus serratus_, n. sp. (Pl. 34, fig. 2).
_Heliostylus serratus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxiv.
fig. 2).
Disk with smooth surface, four times as broad as the medullary shell. Pores
regular, circular; fourteen to sixteen on the radius of the disk. Margin
with a broad solid equatorial girdle, which bears forty to fifty strong
conical teeth on the periphery; teeth about as long as the radius of the
medullary shell. Both opposite marginal spines spindle-shaped, about as
long as the diameter of the disk, and as broad as the girdle.
_Dimensions._--Diameter of the disk 0.3, of the medullary shell 0.075;
length of both main spines 0.2 to 0.3, breadth 0.03.
_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.
5. _Sethostylus hastatus_, n. sp.
Disk with smooth surface, two and a half times as broad as the medullary
shell. Pores irregular, roundish; ten to twelve on the radius of the disk.
Margin with a broad solid equatorial girdle, which bears on the periphery
six conical teeth, three on each half between the two main spines, which
are cylindrical, longer than the diameter of the disk, and half as broad as
the girdle. (This species can be derived from _Heliosestrum_, two opposite
spines of the eight marginal spines being much stronger developed than the
other six.)
_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.06;
length of both main spines 0.2, breadth 0.01.
_Habitat._--North Atlantic, Station 354, surface.
{430}6. _Sethostylus spicatus_, n. sp.
Disk with spiny surface, four times as broad as the medullary shell. Pores
irregular roundish, with many unequal conical spines between them. Margin
with an equatorial girdle, composed of three to four concentric series of
conical radial spines, about as long as the radius of the medullary shell.
Both main spines very large, cylindrical, longer than the diameter of the
disk, and as broad as the radius of the medullary shell.
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05;
length of the main spines 0.3 or more, breadth 0.025.
_Habitat._--Fossil in the rocks of Barbados, Haeckel; living in the depths
of the Equatorial Atlantic, Station 348, depth (2450) fathoms.
Genus 186. _Phacostylus_,[225] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with double medullary shell and with two
radial spines on the margin of the disk, opposite in the equatorial axis.
The genus _Phacostylus_ differs from the foregoing _Sethostylus_ by the
duplication of the medullary shell, and bears the same relation to it as
_Phacodiscus_ does to _Sethodiscus_, or as _Amphicyclia_ in the
Coccodiscida does to _Stylocyclia_.
Subgenus 1. _Phacostylium_, Haeckel.
_Definition._--Margin of the disk simple, smooth, without equatorial
girdle, and without a corona of marginal spines.
1. _Phacostylus amphistylus_, n. sp. (Pl. 31, fig. 12).
Disk with smooth surface, four times as broad as the outer, and twelve
times as broad as the inner medullary shell. Pores regular, circular;
twelve to fourteen on the radius of the disk. Margin of the disk simple,
smooth, without spines and equatorial girdle. Both polar spines conical,
longer than the diameter of the disk, furrowed at the base, and twice as
broad as the inner medullary shell.
_Dimensions._--Diameter of the disk 0.16 to 0.18, of the outer medullary
shell 0.045, of the inner 0.015; length of the polar spines 0.2, basal
breadth 0.03.
_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.
2. _Phacostylus amphixiphus_, n. sp.
Disk with smooth surface, three times as broad as the outer, and eight
times as broad as the inner medullary shell. Pores irregular, roundish; ten
to eleven on the radius. Margin of the disk {431}simple, smooth, without
spines and equatorial girdle. Both polar spines sword-shaped triangular,
two-edged, about as long as the radius of the disk, and as broad at the
base as the inner medullary shell.
_Dimensions._--Diameter of the disk 0.15, of the outer medullary shell
0.05, of the inner 0.02; length of the polar spines 0.08, basal breadth
0.02.
_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.
Subgenus 2. _Astrostylus_, Haeckel.
_Definition._--Margin of the disk with a solid equatorial girdle or a
corona of radial spines.
3. _Phacostylus amphipyramis_, n. sp.
Disk with spiny surface, four and a half times as broad as the outer, and
fourteen times as broad as the inner medullary shell. Pores irregular,
roundish; eight to ten on the radius. Margin of the disk with a corona of
irregular, radial spines. Both opposite polar spines pyramidal, twice as
long as broad, and nearly as long as the radius of the disk.
_Dimensions._--Diameter of the disk 0.22, of the outer medullary shell
0.05, of the inner 0.016; length of the polar spines 0.1, basal breadth
0.05.
_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.
4. _Phacostylus caudatus_, n. sp. (Pl. 32, fig. 6).
_Astrosestrum caudatum_, Haeckel, 1881, Prodromus et Atlas (pl. xxxii.
fig. 6).
Disk with smooth surface, two and a half times as broad as the outer, and
six times as broad as the inner medullary shell. Pores regular, circular;
six to seven on the radius of the disk. Margin with a solid equatorial
girdle, and irregularly bordered with eight to ten conical spines; two
opposite of these are much longer than the others. (This species can be
derived from _Astrosestrum_, two opposite marginal spines being much more
strongly developed than the six to eight others.)
_Dimensions._--Diameter of disk 0.12, of the outer medullary shell 0.05, of
the inner 0.02; length of the polar spines 0.1 to 0.25, basal breadth
0.025.
_Habitat._--North Pacific, Station 244, depth 2900 fathoms.
5. _Phacostylus maximus_, n. sp.
Disk with smooth surface, five times as broad as the outer, and ten times
as broad as the inner medullary shell. Pores regular, circular; twenty to
twenty-two on the radius. Margin with a solid equatorial girdle, bearing on
the periphery one hundred to one hundred and twenty plain teeth, and
two very large polar spines, which are cylindrical, longer than the
diameter of the disk, and as broad at the furrowed base as the radius
of the outer medullary shell. (Similar to _Sethostylus dentatus_,
Pl. 34, fig. 1, but much larger, and with a double medullary shell.)
{432}_Dimensions._--Diameter of the disk 0.4, of the outer medullary shell
0.08, of the inner 0.04; length of the polar spines 0.5, basal breadth
0.04.
_Habitat._--Fossil in the rocks of Barbados.
Genus 187. _Triactiscus_,[226] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with simple medullary shell, and with three
radial spines on the margin of the disk, placed in the equatorial plane.
The genus _Triactiscus_ exhibits on the margin of the lenticular phacoid
shell three radial solid spines, the distance between which is sometimes
equal, at other times unequal. Either all the three spines are of equal
size and similar form, or one odd arm is smaller than the two paired arms.
The triradial form of this genus is repeated in _Tripodocyclia_ among the
Coccodiscida, and in _Tripodictya_ among the Porodiscida. The medullary
shell of _Triactiscus_ is simple.
1. _Triactiscus tripyramis_, n. sp. (Pl. 33, fig. 6).
Disk with smooth surface and smooth margin, three times as broad as the
medullary shell. Pores regular, circular; twelve to thirteen on the radius
of the disk. Three radial spines of nearly equal size and equidistant, or
one odd spine a little smaller, and the opposite angle (between the paired
spines) also smaller. Spines pyramidal, with broad prominent edges, one to
one and a half times as long as the radius of the disk, as broad at the
base as the radius of the medullary shell.
_Dimensions._--Diameter of the disk 0.15; of the medullary shell 0.05,
pores 0.006.
_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.
2. _Triactiscus tricuspis_, n. sp. (Pl. 33, fig. 5).
Disk with smooth surface and smooth margin, five times as broad as the
medullary shell. Pores irregular, roundish; ten to eleven on the radius of
the disk. Three radial spines of unequal size and at unequal distances,
very short, conical, not longer than the radius of the medullary shell.
_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.03;
pores 0.004 to 0.008.
_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.
3. _Triactiscus tripodiscus_, Haeckel.
_Haliomma triactis_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 236, Taf. xxviii. fig, 4.
Disk with thorny surface and spiny margin, three times as broad as the
medullary shell. Pores regular, circular; eight to nine on the radius of
the disk. Three radial spines of different {433}size and at unequal
distances, one odd spine as long as the radius, both paired spines as long
as the diameter of the disk; the odd angle between the latter is smaller.
Spines pyramidal, with broad edges.
_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.05,
pores 0.008.
_Habitat._--Fossil in the rocks of Barbados.
Genus 188. _Sethostaurus_,[227] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with simple medullary shell and with four
radial spines on the margin of the disk, crossed in the equatorial plane.
The genus _Sethostaurus_ exhibits four marginal spines, which form commonly
a more or less regular cross in the equatorial plane. Sometimes the size
and disposition of the four spines become more or less different, and also
the angles between them vary; the regular rectangular cross passes over
into a bilateral or irregular form. The medullary shell is simple. The same
cross-form of the disk is seen in _Staurocyclia_ among the Coccodiscida,
and in _Staurodictya_ among the Porodiscida.
Subgenus 1. _Sethostaurium_, Haeckel.
_Definition._--Margin of the disk without a solid equatorial girdle or a
corona of spines.
1. _Sethostaurus orthostaurus_, n. sp. (Pl. 31, figs. 1, 2).
Disk with smooth surface, three times as broad as the medullary shell.
Pores regular, circular; thirteen to fourteen on the radius of the disk.
Margin simple, smooth, without girdle. Four crossed spines equal,
pommel-shaped, angular, contracted at the base, scarcely as long as the
diameter of the medullary shell.
_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.05;
length of the crossed spines 0.04, breadth 0.02.
_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.
2. _Sethostaurus conostaurus_, n. sp. (Pl. 34, figs. 7, 8).
Disk with spiny surface, three times as broad as the medullary shell. Pores
irregular, roundish; seven to eight on the radius. Margin simple, smooth,
without girdle. Four crossed spines subregular, equal, conical, about as
long as the diameter and as broad at the base as the radius of the
medullary shell. (Fig. 7 exhibits the normal form, fig. 8 an abnormality
with five spines.)
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.06;
length of the crossed spines 0.05, basal breadth 0.03.
_Habitat._--South Atlantic, Station 333, surface.
{434}3. _Sethostaurus rhombostaurus_, n. sp. (Pl. 31, fig. 4).
Disk with smooth surface, two and a half times as broad as the medullary
shell. Pores regular, circular; ten to eleven on the radius. Margin simple,
smooth, without girdle. Two opposite spines longer than the diameter of the
disk, four times as long as the two others, which only equal its radius.
Spines sword-shaped, angular.
_Dimensions._--Diameter of the disk 0.14, of the medullary shell 0.06;
length of the major spines 0.2, of the minor 0.05, breadth 0.025.
_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.
4. _Sethostaurus recurvatus_, n. sp. (Pl. 31, fig. 3).
Disk with smooth surface, three times as broad as the medullary shell.
Pores irregular, roundish; eight to nine on the radius. Margin simple,
smooth, without girdle. Four spines cylindrical, irregularly curved, of
different sizes; one single very large, much longer than the three others;
two opposite lateral spines recurved, hook-shaped.
_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05;
length of the major spine 0.32, of the opposite spine 0.16, of both lateral
spines 0.08.
_Habitat._--South Pacific, Station 295, depth 1500 fathoms.
Subgenus 2. _Heliostaurus_, Haeckel 1881, Prodromus, p. 457.
_Definition._--Margin of the disk with a solid equatorial girdle or a
corona of spines.
5. _Sethostaurus cruciatus_, n. sp. (Pl. 31, fig. 5).
_Heliostaurus cruciatus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxi.
fig. 5).
Disk with smooth surface, three times as broad as the medullary shell.
Pores regular, circular; eleven to twelve on the radius. Margin with a
solid, radially striped girdle, which bears on the periphery forty to fifty
triangular pointed teeth of unequal length. Four crossed spines of equal
size and similar form, pyramidal, sulcated, about as long as the radius of
the disk, as broad at the base as the girdle.
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.06;
length of the crossed spines 0.1, basal breadth 0.02.
_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.
6. _Sethostaurus coronatus_, n. sp.
Disk with spiny surface, twice as broad as the medullary shell. Pores
irregular, roundish; nine to ten on the radius. Margin of the disk with a
solid broad girdle, bearing on the periphery a corona of thirty to forty
flat tongue-shaped teeth of different length. Four crossed spines
{435}prismatic with prominent edges, about as long as the diameter of the
disk, and as broad as the girdle.
_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.08,
length of the crossed spines 0.18, breadth 0.02.
_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.
7. _Sethostaurus gigas_, n. sp.
Disk with smooth surface, four times as broad as the medullary shell. Pores
regular, circular; twenty to twenty-two on the radius. Margin of the disk
with a narrow solid girdle, bearing on the periphery one hundred to one
hundred and twenty slender flat pointed teeth. Four crossed spines equal,
conical, about as long as the radius of the disk, as broad at their
furrowed base as the radius of the medullary shell.
_Dimensions._--Diameter of the disk 0.4, of the medullary shell 0.1; length
of the crossed spines 0.5, basal breadth 0.05.
_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.
Genus 189. _Phacostaurus_,[228] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with double medullary shell and with four
radial spines on the margin of the disk, crossed in the equatorial plane.
The genus _Phacostaurus_ differs from the foregoing _Sethostaurus_ by the
duplication of the medullary shell, and bears to it the same relation as
_Phacodiscus_ does to _Sethodiscus_. Also in this genus the cross of the
shell is commonly regular, rectangular, sometimes more or less irregular.
Subgenus 1. _Phacostaurium_, Haeckel.
_Definition._--Margin of the disk without a solid equatorial girdle or a
corona of spines.
1. _Phacostaurus oceanidum_, n. sp. (Pl. 31, fig. 6).
Disk with smooth surface, three times as broad as the outer and eight times
as broad as the inner medullary shell. Pores regular, circular; eleven to
twelve on the diameter of the disk. Margin smooth. Four crossed spines
pyramidal, deeply sulcate, about as long as the diameter of the outer
medullary shell, and two-thirds as broad at the base.
_Dimensions._--Diameter of the disk 0.15, of the outer medullary shell
0.05, of the inner 0.02; length of the spines 0.05, basal breadth 0.03.
_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.
{436}Subgenus 2. _Astrostaurus_, Haeckel, 1881, Prodromus, p. 457.
_Definition._--Margin of the disk with a solid equatorial girdle, or a
corona of spines.
2. _Phacostaurus quadrigatus_, n. sp.
Disk with smooth surface, four times as broad as the outer and ten times as
broad as the inner medullary shell. Pores irregular, roundish; fifteen to
sixteen on the diameter of the disk. Margin with a broad solid equatorial
girdle, from which arise four crossed spines, conical, as long as the
radius of the disk.
_Dimensions._--Diameter of the disk 0.2, of the outer medullary shell 0.05,
of the inner 0.02; length of the spines 0.1, basal breadth 0.03.
_Habitat._--South Pacific, Station 300, depth 1375 fathoms.
3. _Phacostaurus magnificus_, n. sp. (Pl. 31, figs. 7, 8).
_Astrostaurus magnificus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxi.
figs.7, 8).
Disk with smooth surface, three times as broad as the outer and nine times
as broad as the inner medullary shell. Pores regular, circular; thirteen to
fourteen on the diameter of the disk. Margin with a corona of fifty to
sixty conical spines of unequal length. Four spines of the cross very large
pyramidal, deeply sulcated, longer than the radius of the disk, and as
broad at the base as the radius of the medullary shell.
_Dimensions._--Diameter of the disk 0.22, of the outer medullary shell
0.07, of the inner 0.025; length of the four spines 0.16, basal breadth
0.04.
_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.
Genus 190. _Distriactis_,[229] n. gen.
_Definition._--#Phacodiscida# with simple medullary shell and with six
radial spines on the margin of the disk placed in the equatorial plane.
The genus _Distriactis_ exhibits on the margin of the lenticular phacoid
shell six radial solid spines. Their distance is commonly equal, rarely
unequal. Either all six spines are of equal size and similar form, or three
larger (perradial) alternating with three smaller (interradial), so that
_Distriactis_ appears to be derived from _Triactiscus_ by development of
three secondary between three primary spines.
1. _Distriactis liriantha_, n. sp.
Disk smooth, four times as broad as the medullary shell, with regular,
circular pores (about ten on the radius). Six marginal spines of equal size
and at equal distances, triangular, sulcate, half as long as the radius.
(Similar to _Heliosestrum medusinum_, Pl. 34, fig. 6.)
{437}_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05;
length of the spines 0.05, basal breadth 0.04.
_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.
2. _Distriactis corallantha_, n. sp.
Disk thorny, three times as broad as the medullary shell, with regular,
circular pores, about eight on the radius. Six marginal spines of equal
size and equidistant, conical, nearly as long as the diameter of the disk,
half as broad at the base as the medullary shell.
_Dimensions._--Diameter of the disk 0.12, of the medullary shell 0.04;
length of the spines 0.1, breadth 0.02.
_Habitat._--South Pacific, Station 300, surface.
3. _Distriactis alterna_, n. sp.
Disk smooth, five times as broad as the medullary shell, about twelve pores
on the radius. Six marginal spines pyramidal, at equal distances, but
unequal alternating size; three larger (perradial) spines as long as the
shell radius, three smaller between them (interradial) half as long and
broad.
_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.03;
length of the three major spines 0.08, of the three minor 0.05.
_Habitat._--North Atlantic, Station 353, surface.
4. _Distriactis palmantha_, n. sp.
Disk rough, four times as broad as the medullary shell, about ten pores on
the radius. Six marginal spines conical, at equal distances, but unequal
alternating size; three larger (perradial) spines as long as the shell
diameter, three smaller between them (interradial) as long as the radius.
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05;
length of the three major spines 0.2, of the three minor 0.1,
_Habitat._--South Atlantic, Station 325, surface.
5. _Distriactis amphithecta_, n. sp.
Disk thorny, three times as broad as the medullary shell. Six marginal
spines conical, of very different size; one single (anterior) much larger
than the five others, the opposite (posterior) much smaller. The other four
spines are paired, the anterior pair larger than the posterior.
_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05;
length of the longest spine 0.2, of the shortest 0.04, of the anterior pair
0.1, of the posterior 0.07.
_Habitat._--Indian Ocean, Cocos Islands, surface, Rabbe.
{438}Genus 191. _Heliosestrum_,[230] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with simple medullary shell and with eight
radial spines on the margin of the disk (more or less regularly disposed,
sometimes seven or nine).
The genus _Heliosestrum_ (with simple medullary shell) and the following
_Astrosestrum_ (with double medullary shell) contain those Phacodiscida in
which the margin of the lenticular disk bears eight radial spines, commonly
more or less regularly disposed in the equatorial plane, so that the equal
angles between them amount to 45°. There are, however, many exceptions to
this regular eight-rayed form, either the angles between the eight spines
becoming unequal or the number of the spines amounting to seven or nine
(sometimes also six or ten) in one and the same species. But the regular
form is as prevalent, and also in the abnormal forms indicated by the
position of the spines, that we separate the genus _Heliosestrum_ from
_Heliodiscus_. Both genera are rich in common species, and in some of the
former four perradial (larger) spines alternate regularly with four
interradial (smaller) spines.
Subgenus 1. _Heliosestantha_, Haeckel.
_Definition._--Surface of the disk smooth, without radial spines. Bases of
the marginal spines free, not connected by an equatorial girdle.
1. _Heliosestrum medusinum_, n. sp. (Pl. 34, fig. 6).
_Heliodiscus medusinus_, Haeckel, 1881, Atlas (pl. xxxiv. fig. 6).
Disk with smooth surface, four times as broad as the medullary shell. Pores
regular, circular; about ten on the radius of the disk. Eight marginal
spines regularly distributed (sometimes seven or nine, more or less
irregular), angular, nearly pyramidal (with equilateral triangular
outline), about as long and broad as the diameter of the medullary shell,
without connecting equatorial girdle. From the broad base of each spine run
eight to ten deep furrows convergent to its apex.
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05;
length of the radial spines 0.05, basal breadth 0.05.
_Habitat._--North Pacific, Station 266, surface.
2. _Heliosestrum octastrum_, n. sp.
Disk with smooth surface, three times as broad as the medullary shell.
Pores irregular, roundish; eight to nine on the radius. Eight marginal
spines regularly distributed (sometimes {439}seven or nine, more or less
irregular), conical, about as long as the diameter of the disk, without a
connecting equatorial girdle.
_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05;
length of the radial spines 0.16, basal breadth 0.01.
_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.
3. _Heliosestrum solarium_, Haeckel.
_Haliomma sol_ (_partim_), Ehrenberg, 1875 (_non_ 1844), Abhandl. d. k.
Akad. d. Wiss. Berlin, p. 74, Taf. xxviii. fig. 1.
Surface of the disk smooth; its diameter six times as large as that of the
medullary shell. Pores regular, circular; nine to ten on the radius. Eight
marginal spines regularly distributed (sometimes seven or nine, more or
less irregular), conical, about as long as the diameter of the medullary
shell, without a connecting equatorial girdle.
_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.03;
length of the radial spines 0.03, basal breadth 0.01.
_Habitat._--Fossil in the Tertiary rocks of Barbados.
4. _Heliosestrum liriope_, n. sp.
Surface of the disk smooth; its diameter four times as large as that of the
medullary shell. Pores subregular, circular; seven to eight on the radius.
Eight marginal spines regularly distributed, conical, compressed,
alternating longer and shorter; the longer equal to the diameter of the
disk, the shorter to the radius.
_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.4;
length of the major radial spines 0.15, of the minor 0.09.
_Habitat._--North Pacific, Station 236, surface.
5. _Heliosestrum quadrigeminum_, n. sp.
Surface of the disk smooth; its diameter four times as large as that of the
medullary shell. Pores irregular, roundish; six to seven on the radius.
Eight marginal spines triangular, flat, regularly disposed, alternating
longer and shorter, the major as long as the radius of the shell, and half
as broad at the base, with three to four deep furrows on both sides,
without a connecting equatorial girdle.
_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.04;
length of the larger radial spines 0.08, of the smaller 0.04, basal breadth
0.04.
_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.
6. _Heliosestrum contiguum_, Haeckel.
_Haliomma contiguum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 74, Taf. xxvii. fig. 5.
Disk with smooth surface, four times as broad as the medullary shell.
Pores irregular, roundish, touching, with very thin bars; nine to ten on
the radius. Eight marginal spines (often {440}seven or nine) conical, half
as long as the radius, twice as long as broad, without a connecting
equatorial girdle.
_Dimensions._--Diameter of the disk 0.17, of the medullary shell 0.04;
length of the radial spines 0.04, basal breadth 0.02.
_Habitat._--Fossil in Barbados.
7. _Heliosestrum irregulare_, n. sp.
Disk with smooth surface, four times as broad as the medullary shell. Pores
irregular, roundish; nine to eleven on the radius. Eight conical radial
spines of irregular size and distribution, often seven or nine, about as
long as the radius of the disk (in some cases longer, in others shorter).
No connecting equatorial girdle.
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05;
length of the radial spines 0.1, basal breadth 0.02.
_Habitat._--Central Pacific, Stations 270 to 272, depth 2425 to 2925
fathoms.
Subgenus 2. _Heliosestilla_, Haeckel.
_Definition._--Surface of the disk armed with radial spines. Bases of the
marginal spines free, without a connecting equatorial girdle.
8. _Heliosestrum octonum_, n. sp. (Pl. 34, fig. 3).
Disk with spiny surface, three times as broad as the medullary shell. Pores
circular, of very different sizes; eight to ten on the radius. Eight
conical marginal spines of equal size and equidistant, as long as the
radius of the disk, and one-third as broad at the base as the medullary
shell. Numerous spines on the surface bristle-shaped, on the margin half as
long as the eight main spines, in the central part shorter.
_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.06;
length of the marginal spines 0.1, basal breadth 0.02.
_Habitat._--Central Pacific, Station 271, surface.
9. _Heliosestrum ægineta_, n. sp.
Disk with spiny surface, four times as broad as the medullary shell. Pores
irregular, roundish, of different sizes; twelve to fourteen on the radius.
Eight pyramidal marginal spines regularly disposed, four larger (perradial)
alternating with four smaller (interradial); the former as long as the
radius of the disk, the latter half as long.
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05;
length of the marginal spines 0.05 to 0.1, basal breadth 0.03.
_Habitat._--South Atlantic, Station 330, surface.
{441}Subgenus 3. _Heliosestomma_, Haeckel.
_Definition._--Surface of the disk smooth, without radial spines. Bases of
the marginal spines connected by a solid equatorial girdle.
10. _Heliosestrum octangulum_, n. sp.
Disk with smooth surface, octagonal, twice as broad as the medullary shell.
Pores regular, circular; nine to ten on the radius. Equatorial girdle
narrow, radially striped, connecting the points of the eight short,
regularly disposed, marginal spines in such a manner that the whole shell
forms a regular octagon with rectilinear sides.
_Dimensions._--Diameter of the disk 0.11 to 0.12, of the medullary shell
0.05 to 0.06; length of the sides of the octagon 0.06.
_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.
11. _Heliosestrum octogonium_, n. sp.
Disk with smooth surface, octagonal, four times as broad as the medullary
shell. Pores irregular, roundish; eight to nine on the radius. Equatorial
girdle broad, smooth, connecting the points of the eight short, triangular,
flat marginal spines in such a manner that the whole shell forms a
subregular octagon with concave, nearly equal sides. (Sometimes seven or
nine spines instead of eight are developed.)
_Dimensions._--Diameter of the disk 0.16 to 0.18, of the medullary shell
0.04 to 0.05; length of the radial spines 0.02 to 0.04, basal breadth 0.03.
_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.
12. _Heliosestrum craspedotum_, n. sp.
_Haliomma humboldti_, var., Bury, 1862, Polycystins of Barbados, pl.
viii. fig. 4 (below).
Disk with smooth surface, three times as broad as the medullary shell.
Pores subregular, circular; ten to twelve on the radius. Eight marginal
spines (sometimes seven or nine) triangular, deeply sulcated, half as long
and one-third as broad as the radius of the disk, connected by a narrow,
radially striped equatorial girdle.
_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.06;
length of the radial spines 0.05, basal breadth 0.03.
_Habitat._--Central Pacific, Stations 271 to 274, at various depths, also
fossil in Barbados.
Genus 192. _Astrosestrum_,[231] Haeckel, 1881, Prodromus, p. 457.
_Definition._--#Phacodiscida# with double medullary shell and with eight
radial spines on the margin of the disk (more or less regularly disposed,
sometimes seven or nine).
{442}The genus _Astrosestrum_ differs from the foregoing _Heliosestrum_ by
the duplication of the medullary shell. The eight marginal spines in the
majority of individuals are regularly formed and disposed, of equal size
and equidistant. But there are frequent exceptions to this rule, either the
angles between the eight spines being more or less different, or the number
amounting to seven or nine, instead of eight. Here also in some species
four larger (perradial) spines alternate regularly with four smaller
(interradial spines), after the same law of symmetry, which is common in
the Medusæ.