was founded by him (1860) for one single species, afterwards (1872)
described and figured as _Euchitonia furcata_. Retaining this species
correctly as the type of this genus, I give to it here the above diagnosis.
In my Monograph (1862, p. 503) I described seven Mediterranean species of
_Euchitonia_. Three of these have in common the characters according to the
present diagnosis: _Euchitonia mülleri_, _Euchitonia virchowii_,
_Euchitonia beckmanni_; two others appertain (on account of the regular,
not bilateral form) to _Hymeniastrum_, and two others (on account of the
forked, not simple arms) to _Trigonastrum_. Afterwards (1880) three true
fossil species of _Euchitonia_ were described by Stöhr (_Euchitonia
cruciata_, _Euchitonia zittelii_, and _Euchitonia acuta_). Some species of
this genus are cosmopolitan, and appertain to the most common and
everywhere represented #Discoidea#.
Subgenus 1. _Stylactis_, Ehrenberg, 1872 (_loc. cit._).
_Definition._--Arms with blunt ends, without terminal spines.
1. _Euchitonia furcata_, Ehrenberg.
_Euchitonia furcata_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin, p. 308; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. vi. iii.
fig. 6.
Distance between the paired arms about half as large as their distance from
the odd arm. All three arms nearly of the same size and form, about twice
as long as broad, one and a half times at the {533}blunt convex end as
broad as at the base. Patagium incomplete, with concave chamber-rows and
irregular network, only enveloping the basal half of the arms.
_Dimensions._--Radius of all three arms 0.15, basal breadth of each arm
0.04, terminal breadth 0.06.
_Habitat._--North Pacific, Californian Sea, depth 2600 fathoms, Ehrenberg.
2. _Euchitonia mülleri_, Haeckel.
_Euchitonia mülleri_, Haeckel, 1862, Monogr. d. Radiol., p. 508, Taf.
xxx. figs. 5-10.
_Euchitonia mülleri_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 110, Taf.
v. fig. 5.
Distance between the paired arms about two-thirds as large as their
distance from the odd arm, which is somewhat larger. Length of the arms
equals two and a half times the breadth of the blunt convex end or five
times the breadth of the base. Patagium with concave chamber-rows, nearly
complete, enveloping the arms with exception of the terminal face. (This
common species is very variable; compare my Monograph.)
_Dimensions._--Radius of all three arms 0.16 to 0.22, basal breadth 0.03 to
0.05, terminal breadth 0.06 to 0.08.
_Habitat._--Cosmopolitan; one of the most common #Discoidea# in all seas,
on the surface as well as at different depths; also fossil in the Tertiary
rocks of Barbados and Sicily.
3. _Euchitonia triangulum_, Haeckel.
_Stylactis triangulum_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 320; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. viii.
fig. 9.
_Stylactis triangulum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 113, Taf.
vi. fig. 2.
Distance between the paired arms about two-thirds as large as their
distance from the odd arm. All three arms nearly of the same size and form,
about one and a half times as long as broad, nearly as broad at the base as
at the blunt rounded end. Patagium incomplete, with convex chamber-rows,
enveloping about two-thirds of the arms.
_Dimensions._--Radius of all three arms 0.15, basal breadth 0.05, terminal
breadth 0.06.
_Habitat._--Pacific and Atlantic, Stations 253, 272, 354, surface; also
fossil in the Tertiary rocks of Barbados and Sicily.
4. _Euchitonia cruciata_, Stöhr.
_Euchitonia cruciata_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 111, Taf.
v. fig. 7.
Distance between the paired arms about one and a half times as large as
their distance from the odd arm, which is a little larger. Length of the
arm nearly equals twice the breadth, which is the same at the base and at
the rounded blunt ends. Patagium incomplete, with concave chamber-rows,
enveloping only the base of the arms, and forms between them three other
smaller arms; therefore the whole shell forms six angles with six
alternating arms.
_Dimensions._--Radius of all three arms 0.15, basal breadth 0.05.
_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.
{534}5. _Euchitonia lanceolata_, n. sp. (Pl. 43, fig. 9).
Distance between the paired arms about one and a third times as large as
their distance from the odd arm. All three arms nearly of the same size and
form, three times as long as broad, lanceolate, much broader in the middle
part than at both ends; distal end cuspidate, but not spiny. Patagium
incomplete, with convex chamber-rows, envelops about two-thirds of the
arms.
_Dimensions._--Radius of all three arms 0.18, greatest breadth (in the
width) 0.06.
_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.
6. _Euchitonia zittelii_, Haeckel.
_Stylactis zittelii_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 112, Taf.
v. fig. 8.
Distance between the paired arms about one-fifth as large as their distance
from the odd arm. All three arms nearly of the same size and form, in the
proximal half thinner and nearly square, in the distal half thicker and
circular; the latter half twice to three times as broad as the former.
Patagium incomplete, with convex chamber-rows, envelops only the proximal
square half of the arms.
_Dimensions._--Radius of all three arms 0.15, basal breadth 0.03, terminal
breadth 0.08.
_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.
7. _Euchitonia stöhrii_, n. sp. (Pl. 43, fig. 12).
Distance between the paired arms about four-fifths as large as their
distance from the odd arm, which is one and a half times as long as the
former. Arms about three times as long as broad, twice as broad in the
distal half as in the proximal half, with rounded blunt ends. Patagium
complete, with concave chamber-rows, enveloping the whole shell, also the
ends of the arms.
_Dimensions._--Radius of the paired arms 0.2, of the odd arm 0.25; basal
breadth 0.03, distal breadth 0.06.
_Habitat._--Fossil in the rocks of Barbados and of Nicobar Islands,
Haeckel. Indian Ocean, Cocos Islands (Rabbe). Also in the Central Pacific,
Station 267.
8. _Euchitonia beckmannii_, Haeckel.
_Euchitonia beckmannii_, Haeckel, 1862, Monogr. d. Radiol., p. 505, Taf.
xxxi. fig. 1.
Distance between the paired arms scarcely half as large as their distance
from the odd arm, which is somewhat larger. Each arm with six simple broad
chambers (without radial septa), the terminal chambers semilunar, convex,
blunt, four times as broad as the first (basal) chamber. Patagium
incomplete, with convex chamber-rows, enveloping the arms with exception of
the broad blunt terminal face.
_Dimensions._--Radius of the paired arms 0.15, of the odd arm 0.18; basal
breadth 0.02 to 0.03, terminal breadth 0.1 to 0.15.
_Habitat._--Mediterranean (Messina), Haeckel, surface.
{535}9. _Euchitonia virchowii_, Haeckel.
_Euchitonia virchowii_, Haeckel, 1862, Monogr. d. Radiol., p. 503, Taf.
xxx. figs. 1-4.
_Histiastrum fasciatum_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin, p. 842.
Distance between the paired arms about half as large as their distance from
the odd arm, which is somewhat larger. Each arm with six broad chambers,
bisected by a radial septum; the terminal chamber convex, blunt, twice as
broad as the basal chamber. Patagium incomplete, with concave chamber-rows,
enveloping the arms with exception of the broad blunt terminal face.
_Dimensions._--Radius of the paired arms 0.15, of the odd arm 0.16; basal
breadth 0.05, terminal breadth 0.1 to 0.12.
_Habitat._--Mediterranean (Messina), Atlantic (Canary Islands).
Subgenus 2. _Pteractis_, Ehrenberg, 1872 (_loc. cit._).
_Definition._--Arms provided with radial spines at the distal end.
10. _Euchitonia elegans_, Haeckel.
_Pteractis elegans_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 299, Taf. viii. fig. 3.
Distance between the paired arms half as large as their distance from the
odd arm. This latter is straight, while both the former are concavely
curved towards the middle line. Arms five times as long as broad, at the
distal end pointed and armed with a short conical terminal spine. Patagium
nearly complete, enveloping four-fifths of the arms, with four to five
concave chamber-rows.
_Dimensions._--Radius of the arms 0.2, breadth of them 0.03.
_Habitat._--Tropical Pacific, Philippine Sea, depth 3300 fathoms
(Ehrenberg).
11. _Euchitonia carcinus_, n. sp. (Pl. 43, fig. 10).
Distance between the paired arms scarcely one-fourth as great as their
distance from the odd arm. This latter is straight, twice as long as the
former, which are concavely curved towards the middle line. The odd arm is
three times as broad at the distal end as at the narrow base. The end of
each arm is furnished with a strong triangular radial spine and a group of
smaller spines. Patagium incomplete, with two to three concave
chamber-rows, enveloping only the basal half of the arms.
_Dimensions._--Radius of the paired arms 0.15, breadth 0.03; radius of the
odd arm 0.3, breadth on its base 0.02, on its distal end 0.07.
_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.
{536}12. _Euchitonia acuta_, Stöhr.
_Euchitonia acuta_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 111, Taf. v.
fig. 6.
Distance between the paired arms two-thirds as great as their distance from
the odd arm. All three arms nearly of the same size and form, two and a
half times as long as broad, nearly lanceolate, at their broadest part one
and a half times as broad as at their base. Patagium complete, enveloping
the whole triangular disk, with five to six concave chamber-rows. In the
figure of Stöhr the ends of the arms are simply pointed, while I find in
the same fossil form a short terminal conical spine.
_Dimensions._--Radius of all three arms 0.14; breadth at the base 0.04, at
the broadest part 0.06.
_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte (Stöhr),
Caltanisetta (Haeckel).
13. _Euchitonia ypsiloides_, Haeckel.
_Histiastrum ypsiloides_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 843.
Distance between the paired arms two-thirds as great as their distance from
the odd arm, which is somewhat larger. Length of the arms equals five times
the breadth of the narrow base, which is half that of the distal end; this
latter is armed with three to five short conical spines. Patagium complete,
with six to seven concave chamber-rows, enveloping the whole arms with the
exception of the terminal spines. (Differs from _Euchitonia mülleri_ almost
solely by the possession of terminal spines.)
_Dimensions._--Radius of the arms 0.18 to 0.2; breadth at the base 0.04, at
the distal end 0.08.
_Habitat._--Mediterranean (Messina), Atlantic (Canary Islands), surface.
14. _Euchitonia echinata_, n. sp. (Pl. 43, fig. 11).
Distance between paired arms three-fourths as great as their distance from
the odd arm, which is somewhat larger. Arms one and a half times as long as
broad, somewhat constricted in the middle part, armed at the rounded ends
with numerous (thirty to forty) strong, conical spines. Patagium complete,
with four or five rectilinear parallel chamber-rows, enveloping the whole
of the arms with the exception of the spiny ends.
_Dimensions._--Radius of the arms (without spines) 0.2, breadth 0.06 to
0.09.
_Habitat._--North Pacific, Station 253, depth 3125 fathoms.
Genus 231. _Chitonastrum_,[270] Haeckel, 1881, Prodromus, p. 460.
_Definition._--#Porodiscida# with three forked, chambered arms, without a
patagium. (Arms and angles between them either equal or unequal.)
The genus _Chitonastrum_ differs from its ancestral form, _Dictyastrum_, by
the bifurcation of the distal ends of the arms. The few species of this
genus are partly {537}regular (like _Dictyastrum_), partly bilateral (like
_Rhopalastrum_). If the number of species increases much, these two
subgenera may be separated into two genera: _Chitonastrella_ corresponding
to the former, _Chitonastromma_ to the latter.
Subgenus 1. _Chitonastrella_, Haeckel.
_Definition._--All three arms of the same size and form, equidistant;
fundamental form of the shell therefore an equilateral triangle.
1. _Chitonastrum triglochin_, n. sp.
All three arms equal and equidistant. Each arm has the form of an isosceles
triangle, twice as high as broad; the truncated apex of the triangle is
inserted into the large central disk, whilst its distal base (four times as
broad) is divided by a deep incision (half as long as the arm). Each arm
with ten to twelve joints, simple in its basal half, double in its distal
half. Axes of the six branches straight. (Resembles _Trigonastrum
regulare_, Pl. 43, fig. 16, but differs in the absence of a patagium.)
_Dimensions._--Radius of each arm 0.24, greatest breadth 0.11, basal
breadth 0.03.
_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.
2. _Chitonastrum bathybium_, n. sp.
All three arms equal and equidistant, in the basal two-thirds simple,
rectilinear, three times as long as broad, in the distal third forked, both
branches equal, straight, blunt, half as broad as the basal part.
_Dimensions._--Radius of each arm 0.18, basal breadth 0.04, breadth of the
branches 0.02.
_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.
Subgenus 2. _Chitonastromma_, Haeckel.
_Definition._--One odd arm different in size or form from the two other
arms, which are paired; distance between them different; fundamental form
of the shell therefore a bilateral, isosceles triangle.
3. _Chitonastrum jugatum_, n. sp. (Pl. 43, fig. 14).
_Dictyastrum jugatum_, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig.
14).
Arms very different; odd arm club-shaped, twice as long as broad, at the
blunt distal end twice as broad as at the base; its axis is perpendicular
to the common axis of both paired arms, which are only two-thirds as long,
not so broad, and in the distal half divided into two branches; the
anterior branch is straight, nearly horizontal, the posterior shorter and
curved backwards.
{538}_Dimensions._--Radius of the odd arm 0.2, of the paired arms 0.15;
distal breadth of the former 0.08, basal breadth 0.04; breadth of the
paired arms 0.04.
_Habitat._--South Atlantic, Station 325, surface.
4. _Chitonastrum dicranoides_, n. sp.
All three arms in the basal half simple, nearly square, in the distal half
forked; branches straight, blunt. Odd arm twice as large as the paired
arms; angle between the latter larger than the angles between them and the
odd arm. (The form of the arms resembles _Dicranastrum furcatum_, Pl. 47,
fig. 2.)
_Dimensions._--Radius of the odd arm 0.24, of the paired arms 0.12; basal
breadth 0.06.
_Habitat._--North Atlantic, Station 353, surface.
5. _Chitonastrum lyra_, n. sp. (Pl. 43, fig. 15).
_Dictyastrum lyra_, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig.
15).
All three arms forked and nearly of the same size, but different in form
and position. The distance between the branches of the two paired arms is
only one-fourth of the distance between them and the odd arm. Each arm in
the basal two-thirds is simple, with eleven to twelve transverse septa, in
the distal third forked, each branch with four to five transverse septa.
The branches of each arm are curved convexly one to another, ending
obtusely. The axis of the simple proximal part is straight in the odd arm,
in the paired arms curved concavely towards the middle line. In the figured
specimen, which I observed living in Portofino (in September 1880), the
central chamber of the central disk and the first surrounding ring were
filled with the nucleus of the cell; both external rings were filled (like
all chambers of the arms) with pink oil-globules of the red central
capsule. From the mantle, enveloping the shell, radiated innumerable fine
pseudopodia (much too short in the figure), and between the two paired arms
a long "sarcode-flagellum."
_Dimensions._--Radius of each arm 0.16; greatest breadth of the odd arm
0.04; basal breadth of the paired arms 0.02; distance of both branches of
each arm 0.08.
_Habitat._--Mediterranean, Portofino, near Genoa, Haeckel.
Genus 232. _Trigonastrum_,[271] n. gen.
_Definition._--#Porodiscida# with three forked, chambered arms, connected
by a patagium. (Arms and angles between them either equal or unequal.)
The genus _Trigonastrum_ differs from the preceding _Chitonastrum_, its
ancestral form, in the development of a patagium between the arms. It bears
therefore to the latter the same relation that _Euchitonia_ does to
_Rhopalastrum_.
{539}Subgenus 1. _Trigonastrella_, Haeckel.
_Definition._--All three arms of the same size and form, equidistant;
fundamental form of the shell therefore a regular, equilateral triangle.
1. _Trigonastrum regulare_, n. sp. (Pl. 43, fig. 16).
_Chitonastrum regulare_, Haeckel, 1881, Prodromus et Atlas (pl. xliii.
fig. 16).
All three arms equal and equidistant. Each arm has the form of an isosceles
triangle, twice as high as broad, the truncated apex of which is inserted
into the large circular central disk, whilst its distal base (four times as
broad) is divided by a deep incision (half as long as the arm). Each arm
with ten to twelve joints. Patagium between the arms nearly complete,
spongy. (Differs from _Chitonastrum triglochin_ mainly in the possession of
a patagium.)
_Dimensions._--Radius of each arm 0.24, greatest breadth 0.11, basal
breadth 0.03; length of the sides of the regular triangle 0.45.
_Habitat._--Pacific, central area, Station 274, surface.
Subgenus 2. _Trigonastromma_, Haeckel.
_Definition._--One odd arm different in form or size from the other two
arms, which are paired; distance between them different; fundamental form
of the shell therefore an isosceles triangle.
2. _Trigonastrum krohnii_, Haeckel.
_Euchitonia krohnii_, Haeckel, 1862, Monogr. d. Radiol., p. 507.
All three arms different; distance between the two paired arms smaller than
their distance from the odd arm. Odd arm with six joints. Each paired arm
with seven joints, increasing in breadth towards the distal end. Odd arm
and one paired arm forked at the end, the other paired arm simple. Patagium
nearly complete. (The asymmetry in this form may perhaps be an individual
anomaly, as also in _Myelastrum anomalum_, Pl. 47, fig. 9.)
_Dimensions._--Radius of the arms about 0.13 to 0.16, breadth 0.05 to 0.08.
_Habitat._--North Atlantic, Funchal, Madeira, Krohn, surface.
3. _Trigonastrum gegenbauri_, Haeckel.
_Euchitonia gegenbauri_, Haeckel, 1862, Monogr. d. Radiol., p. 506, Taf.
xxxi. figs. 2, 3.
Arms different; distance between the paired arms larger than their distance
from the odd arm, which is one-third shorter. Odd arm egg-shaped, simple,
with seven joints, undivided. Both paired arms equal, with ten joints, in
the distal third forked. Patagium nearly complete.
_Dimensions._--Radius of the odd arm 0.14, greatest breadth 0.08; radius of
the paired arms 0.2.
_Habitat._--Mediterranean (Messina), Haeckel, surface.
{540}Genus 233. _Stauralastrum_,[272] n. gen.
_Definition._--#Porodiscida# with four simple, undivided, chambered arms,
without a patagium; quadrangular shell a regular cross, with four equal
arms placed at right angles.
The genus _Stauralastrum_ is the most simple form of the Tessarastrida, or
of those Porodiscida in which the margin of the central disk is armed with
four chambered arms. In _Stauralastrum_ these four arms are quite simple
and equal, without a patagium, separated by four right angles, so that the
whole shell represents a regular rectangular cross. If we connect the
distal points of the arms by lines, we get a complete square. (In my
Prodromus, 1881, the species of this genus were united with _Hagiastrum_,
which genus I now retain for the simple bilateral Tessarastrida.)
Subgenus 1. _Stauralastrella_, Haeckel.
_Definition._--Ends of the arms blunt, without terminal spines.
1. _Stauralastrum cruciforme_, n. sp. (Pl. 45, fig. 6).
Arms very thin, nearly linear, four to five times as long as broad, of
equal breadth at the base and at the truncated distal end; their breadth
equals one-third of the radius of the central disk. Edges of the arms
parallel.
_Dimensions._--Radius of each arm 0.8, breadth 0.016.
_Habitat._--South Pacific, Station 293, surface.
2. _Stauralastrum lanceolatum_, n. sp.
Arms lanceolate, three times as long as broad, in their middle part three
times as broad as at both ends; their greatest breadth nearly equals the
diameter of the central disk. (The arms have the same form as in
_Euchitonia lanceolata_, Pl. 43, fig. 9.) Edges of the arms convex.
_Dimensions._--Radius of each arm 0.3, greatest breadth (in the middle
part) 0.08.
_Habitat._--Pacific, central area, Station 273, depth 2350 fathoms.
3. _Stauralastrum ordo_, n. sp.
Arms trapezoid, about as long as broad, twice as broad at their truncated
distal end as at the base; their basal breadth equals the radius of the
central disk, which exhibits two to three rings. (The arms have nearly the
same form as those in _Hagiastrum mosis_, Pl. 45, fig. 3.) Edges of the
arms rectilinear, divergent towards the ends.
_Dimensions._--Radius of each arm 0.12, basal breadth 0.04, distal breadth
0.08.
_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.
{541}4. _Stauralastrum clavigerum_, n. sp.
Arms twice as long as broad, in their distal half lenticular, nearly
circular, twice as broad as in their square proximal half; their distal
breadth equals the diameter of the central disk, which exhibits three to
four rings. Edges of the arms concave.
_Dimensions._--Radius of each arm 0.2, basal breadth 0.04, distal breadth
0.08.
_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.
5. _Stauralastrum dilatatum_, n. sp.
Arms of nearly equal length and breadth, at their convex distal end three
times as broad as at their narrow base; their distal breadth three times as
large as the radius of the central disk, which exhibits three to four
rings. (Resembles _Histiastrum quadrigatum_, Pl. 46, fig. 3, but has no
patagium.) Edges of the arms concave.
_Dimensions._--Radius of each arm 0.15, basal breadth 0.04, terminal
breadth 0.12.
_Habitat._--South Pacific, Station 300, depth 1375 fathoms.
Subgenus 2. _Stauralastromma_, Haeckel.
_Definition._--Ends of the arms with one or more terminal spines.
6. _Stauralastrum rhopalophorum_, n. sp. (Pl. 45, fig. 1).
_Hagiastrum rhopalophorum_, Haeckel, 1881, Prodromus, p. 460.
Arms cylindrical, eight times as long as broad at their base, at their
distal end club-shaped, three times as broad as at their base; their distal
breadth twice as large as the diameter of the central disk, which exhibits
two to three rings. Surface thorny, with larger spines towards the end, and
one radial, very strong, angular terminal spine. Edges of the arms
parallel.
_Dimensions._--Radius of each arm (without terminal spine) 0.32, basal
breadth 0.03, terminal breadth 0.1.
_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.
7. _Stauralastrum antiquum_, n. sp.
_Rhopalastrum_ sp. Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 5.
Arms six times as long as broad at their base, in their distal half nearly
spherical, three times as broad as in their cylindrical basal half; their
distal breadth nearly equals the diameter of the central disk which
exhibits three to four rings. On the end of each arm one strong, angular,
terminal spine. (Differs from the preceding species by larger central disk
and stouter arms, also by less developed spines.) Edges of the arms
parallel.
_Dimensions._--Radius of each arm 0.25, basal breadth 0.04, terminal
breadth 0.12.
_Habitat._--Fossil in the Barbados rocks; and living in the depths of the
Central Pacific, Station 266, depth 2750 fathoms.
{542}8. _Stauralastrum staurolonche_, n. sp.
Arms four times as long as broad at their base, gradually increasing
towards their truncated end, which is one and a half times as broad as
their base; their distal breadth equals the radius of the central disk,
which exhibits four to five rings. At the end of each arm is a very strong
conical terminal spine. (Resembles _Histiastrum quaternarium_, _Abhandl. k.
Akad. Wiss. Berlin_, 1875, Taf. xxiv. fig. 3, but has no patagium.) Edges
of the arms rectilinear, divergent.
_Dimensions._--Radius of each arm 0.25, basal breadth 0.045, distal breadth
0.07.
_Habitat._--Fossil in the Barbados rocks; and living in the depth of the
Equatorial Atlantic, Station 348, depth (2450) fathoms.
9. _Stauralastrum horridum_, n. sp.
Arms three times as long as broad at their base, gradually increasing
towards their rounded end, which is twice as broad as their base, their
distal breadth equals the diameter of the central disk, which exhibits four
to five rings. Surface thorny, at the distal end of each arm is a group of
twenty to twenty-five smaller and five to six larger, straight, conical
spines. Edges of the arms rectilinear, divergent.
_Dimensions._--Radius of each arm 0.15, basal breadth 0.05, distal breadth
0.1.
_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.
Genus 234. _Hagiastrum_,[273] Haeckel, 1881, Prodromus, p. 460.
_Definition._--#Porodiscida# with four simple, undivided, chambered arms,
without a patagium; quadrangular shell bilateral, two opposite arms of the
main axis (or principal arms) different from the two others (or lateral
arms).
The genus _Hagiastrum_, as here defined, was formerly united by me with the
foregoing _Stauralastrum_, but differs from it by the bilateral or
symmetrical form. Whilst in the latter all four arms and the four angles
between them are equal, they are here differentiated into pairs.
Subgenus 1. _Hagiastrella_, Haeckel.
_Definition._--Both longitudinal arms of equal size and form.
1. _Hagiastrum buddhae_, n. sp. (Pl. 45, fig. 5).
Cross rectangular. Both longitudinal arms of equal size, twice as long as
the transverse arms; all arms smooth, club-shaped, twice as broad at their
globose distal part as at their base, each with three large conical
terminal spines.
{543}_Dimensions._--Radius of the principal arms 0.4, of the lateral arms
0.2; basal breadth 0.06, distal breadth 0.12.
_Habitat._--Indian Ocean, Belligemma, Ceylon, surface, Haeckel.
2. _Hagiastrum bramae_, n. sp.
Cross rectangular. Both longitudinal arms of equal size, one and a half
times as long as the transverse arms; all arms thorny, club-shaped, at
their pear-shaped distal part three times as broad as at their base,
provided with numerous conical spines, one larger terminal spine at their
distal point. (Resembles _Stauralastrum rhopalophorum_, Pl. 45, fig. 1, but
is distinguished by the different size of the arm-pairs, and by the
stronger spines.)
_Dimensions._--Radius of the principal arms 0.3, of the lateral arms 0.2;
basal breadth 0.04, distal breadth 0.12.
_Habitat._--Indian Ocean, off Maldive Islands, surface, Haeckel.
Subgenus 2. _Hagiastromma_, Haeckel.
_Definition._--The two longitudinal arms different in size or form.
3. _Hagiastrum mosis_, n. sp. (Pl. 45, fig. 3).
Cross rectangular. All four arms nearly isosceles, triangular, at their
narrow base half as broad as at their truncated, concavely fluted, distal
end. The posterior principal arm with twelve to thirteen joints, twice as
long as the anterior arm, which has six to seven joints and is one and a
half times as long as the two lateral arms (with four to five joints).
_Dimensions._--Radius of the posterior arm 0.3, of the anterior 0.15, of
the lateral arms 0.1; basal breadth 0.05, terminal breadth 0.1.
_Habitat._--Mediterranean (Smyrna), surface, Haeckel.
4. _Hagiastrum mohammedis_, n. sp.
Cross with unequal angles, the anterior little smaller than the posterior.
All four arms club-shaped, thorny, three times as broad at their globose
distal end as at their narrow base, and furnished with ten to twelve
conical spines. Posterior principal arm twice as long as the anterior, and
four times as long as the rudimentary lateral arms.
_Dimensions._--Radius of the posterior arm 0.4, of the anterior 0.2, of the
lateral arms 0.1; basal breadth 0.02 to 0.03, distal breadth 0.06 to 0.1.
_Habitat._--Philippine Sea, Samboangan, Station 200, surface.
5. _Hagiastrum christi_, n. sp.
Cross with unequal angles, the anterior somewhat smaller than the
posterior. All four arms of similar form, lanceolate, in their middle twice
as broad as at either obtuse end. The posterior {544}principal arm with
twelve joints, one and a half times as long as the anterior (with nine
joints) and twice as long as the two lateral arms (each with six joints).
The form and structure of the arms in this species are nearly the same as
in _Tessarastrum straussi_ (Pl. 45, fig. 8); but the arms are broader in
the middle, and are not connected by a patagium.
_Dimensions._--Radius of the principal posterior arm 0.2, of the anterior
0.15, of each lateral arm 0.1; greatest breadth (in the width) 0.01, basal
breadth 0.03.
_Habitat._--North Atlantic, Færöe Channel, Gulf Stream, surface, John
Murray.
Genus 235. _Histiastrum_,[274] Ehrenberg, 1847, Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, p. 54.
_Definition._--#Porodiscida# with four simple, undivided, chambered arms,
connected by a patagium; square shell a regular cross, with four equal arms
and four right angles between them.
The genus _Histiastrum_, quite insufficiently characterised by Ehrenberg
(1847), was afterwards (1875) illustrated by the figures of two different
fossil species. One of these, _Histiastrum ternarium_, with three arms,
belongs to _Hymeniastrum_; the other, _Histiastrum quaternarium_, is here
retained as the true, typical representative species of the genus. It
differs from its ancestral form _Stauralastrum_, by the possession of a
patagium, from _Tessarastrum_ by the regular square form of the shell.
Subgenus 1. _Histiastrella_, Haeckel.
_Definition._--Distal ends of the arms blunt, without terminal spines.
1. _Histiastrum quadrigatum_, n. sp. (Pl. 46, fig. 3).
Arms at their distal end nearly as broad as long, and four times as broad
as at their narrow base; their lateral edges concave, their terminal edge
convex, without spines. Each arm is divided by seven to eight convex
transverse septa into eight to nine simple, broad chambers. Central disk
with three to four rings, about as broad as the fifth chamber. Patagium
complete, connecting all the lateral edges of the arms.
_Dimensions._--Radius of each arm 0.15, basal breadth 0.03, terminal
breadth 0.12.
_Habitat._--Equatorial Atlantic, Station 347, surface.
2. _Histiastrum excisum_, n. sp.
Arms four times as long as broad at their base, and twice as broad at their
rounded blunt distal end as at their base; their lateral edges rectilinear,
divergent. Central disk with three to four rings, {545}somewhat broader
than their distal end. Patagium incomplete, connecting only the basal half
of the arms, with three to four concave chamber-rows, on the margin
concave. (May be regarded as _Euchitonia mülleri_, with four arms.)
_Dimensions._--Radius of each arm 0.2, basal breadth 0.05, distal breadth
0.1.
_Habitat._--Atlantic, surface, Canary Islands.
3. _Histiastrum velatum_, n. sp. (Pl. 46, fig. 4).
_Dictyastrum velatum_, Haeckel, 1879, Atlas (pl. xlvi. fig. 4).
Arms pear-shaped, rapidly increasing from their narrow base, nearly
circular, little longer than broad; each with eight to nine transverse
chamber-rows; their lateral edges at their base concave, at their end
circular. Central disk with three to four rings, somewhat smaller than one
arm. Patagium complete, with six to seven radial beams, filling out
perfectly the intervals between the arms. A peculiar girdle of finer
network and equal breadth surrounds the whole equatorial periphery of the
disk, and gives it the appearance of a square with rounded corners.
_Dimensions._--Radius of each arm 0.2, basal breadth 0.03, distal breadth
0.12.
_Habitat._--South Atlantic, Station 330, surface.
Subgenus 2. _Histiastromma_, Haeckel.
_Definition._--Distal ends of the arms spiny, furnished with one or more
terminal spines.
4. _Histiastrum quaternarium_, Ehrenberg.
_Histiastrum quaternarium_, Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 74, Taf. xxiv. figs. 3, 4.
Arms six times as long as broad at their base, with rectilinear, little
divergent edges; at their truncated distal end a little broader, with one
single, very strong, conical, terminal spine. Central disk with four to
five rings, somewhat broader than the arm. Patagium incomplete, enveloping
only the basal half of the arms.
_Dimensions._--Radius of each arm 0.18, basal breadth 0.03, distal breadth
0.05.
_Habitat._--Fossil in the rocks of Barbados.
5. _Histiastrum gladiatum_, n. sp.
_Astromma_ sp., Bury, 1862, Polycystins of Barbados, pl. v. fig. 1.
Arms triangular, eight times as long as broad at their base; at their
distal end three times as broad as at their base, with rectilinear,
divergent edges; their truncated end with a large conical, terminal spine.
Central disk with four to five rings, broader than the arms. Patagium
incomplete, enveloping only the basal half of the arms.
{546}_Dimensions._--Radius of each arm 0.12, basal breadth 0.013, distal
breadth 0.04.
_Habitat._--Fossil in the rocks of Barbados; and living in the depth of the
Central Pacific, Station 268, depth 2900 fathoms.
6. _Histiastrum boseanum_, n. sp. (Pl. 46, fig. 1).
Arms linear, twelve times as long as broad at their base (at their distal
end twice as broad as at their base), with rectilinear, parallel edges. The
club-shaped end thickened, dentate, with two lateral rows of strong teeth
in the equatorial plane, and with one very stout, angular, terminal spine.
Central disk with two to three rings, broader than the arms. Patagium
incomplete, with four to five concave chamber-rows, enveloping only the
basal half of the arms. I call this splendid species in honour of Dr. Graf
Bose, the great friend of nature and patron of the University of Jena.
_Dimensions._--Radius of each arm 0.25, basal breadth 0.02, distal breadth
0.05.
_Habitat._--Indian Ocean, Madagascar, Rabbe.
7. _Histiastrum coronatum_, n. sp.
_Stephanastrum_ sp., Bury, 1862, Polycystins of Barbados, pl. iv. fig. 1.
Arms linear, eight times as long as broad, with rectilinear parallel edges;
the thickened, nearly spherical, distal end three times as broad, with five
strong conical spines, one middle (perradial) larger and two smaller on
each side of it. Central disk with two to three rings, of the same breadth
as the terminal knot of the arms. Patagium incomplete, square, enveloping
the arms, with the exception of the knot.
_Dimensions._--Radius of each arm 0.16, basal breadth 0.02, terminal
breadth 0.06.
_Habitat._--Fossil in the rocks of Barbados.
8. _Histiastrum circulare_, n. sp.
_Stephanastrum_ sp., Bury, 1862, Polycystins of Barbados, pl. xxiii. fig.
1.
Arms linear in their inner half, egg-shaped and three times as broad in
their outer half, with ten to twelve strong terminal spines, the middle
(perradial) larger, in all three times as long as broad. Central disk with
three to four rings, broader than their distal knobs. Patagium nearly
complete, circular, enveloping the whole arms, with exception of the
outermost end.
_Dimensions._--Radius of each arm 0.22, basal breadth 0.02, terminal
breadth 0.06.
_Habitat._--Fossil in the rocks of Barbados; and living in the depths of
the Central Pacific, Station 268, depth 2900 fathoms.
9. _Histiastrum pentadiscus_, n. sp. (Pl. 46, fig. 2).
Arms in their inner half linear, twice as long as broad, in their outer
half circular, three times as broad, with the same structure as the central
disk, exhibiting three concentric rings around one {547}central chamber.
Patagium complete, spongy, with radiating beams, enveloping the whole disk,
with the exception of the outermost end of the arms, which is armed with
twelve to sixteen strong conical spines, the middle (perradial) spine much
larger.
_Dimensions._--Radius of each arm (without terminal spine) 0.18, basal
breadth 0.025, terminal breadth 0.08.
_Habitat._--South Atlantic, Station 333, surface.
Genus 236. _Tessarastrum_,[275] n. gen.
_Definition._--#Porodiscida# with four simple, undivided, chambered arms,
connected by a patagium; quadrangular shell bilateral, two opposite arms of
the main axis (or principal arms) different from the two others (or lateral
arms).
The genus _Tessarastrum_, formerly united by me with _Histiastrum_, differs
from the latter in its bilateral or symmetrical form, and bears therefore
the same relation to it that _Hagiastrum_ does to _Stauralastrum_.
Subgenus 1. _Tessarastrella_, Haeckel.
_Definition._--Both longitudinal arms of equal size and form.
1. _Tessarastrum straussii_, n. sp. (Pl. 45, fig. 8).
_Histiastrum straussii_, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig.
8).
Cross not rectangular. Both principal arms of equal size and form, four
times as long as broad, and twice as long as the broader lateral arms; the
former with ten to eleven, the latter with five to six joints, separated by
convex transverse septa. Distal ends of the arms blunt. Axes of the smaller
arms not perpendicular to that of the larger arms; therefore the anterior
angles between them smaller than the posterior angles. Patagium between the
arms incomplete. I call this remarkable species after the great German
philosopher David Strauss.
_Dimensions._--Radius of the principal arms 0.24, of the lateral arms 0.12;
greatest breadth (in the middle) of the former 0.05, of the latter 0.06.
_Habitat._--North Pacific, _Hyalonema_-ground, March 5, 1875.
2. _Tessarastrum spinozæ_, n. sp.
Cross rectangular. Both principal arms of equal size and form, ten times as
long as broad, and twice as long as the lateral arms, which are only five
times as long as broad. All arms linear, at their distal end club-shaped,
and armed with twenty to thirty very strong angular spines. Patagium
incomplete, enveloping only the basal half of the arms. (Resembles
_Histiastrum boseanum_, {548}Pl. 46, fig. 1, but differs in the broader
arms and the unequal size of both pairs.) I call this species after the
great monistic philosopher Benedictus Spinoza.
_Dimensions._--Radius of the principal arms 0.3, of the lateral arms 0.16;
basal breadth 0.025, distal breadth 0.05.
_Habitat._--South Atlantic, Station 333, surface.
3. _Tessarastrum brunonis_, n. sp. (Pl. 45, fig. 9).
_Histiastrum brunonis_, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig.
9).
Cross rectangular. Both principal arms of equal size and form, three times
as long as broad, each with ten joints, three times as long as the lateral
arms, which are nearly square, with four joints. All arms rounded, at their
truncated end little broader than at their base. No spines. Patagium
complete, envelops the whole shell, and is composed of two parallel
lattice-lamellæ on each side of the flat disk, which are connected by very
fine perpendicular bars. This is shown clearly in fig. 9, Pl. 45, where the
disk is seen from the edge. I call this species after the great Italian
philosopher Giordano Bruno.
_Dimensions._--Radius of the principal arms 0.22, of the lateral arms 0.12;
basal breadth 0.04, distal breadth 0.05.
_Habitat._--South Pacific, Station 285, depth 2375 fathoms.
Subgenus 2. _Tessarastromma_, Haeckel.
_Definition._--The two principal arms of different size or form.
4. _Tessarastrum democriti_, n. sp. (Pl. 45, fig. 7).
_Histiastrum democriti_, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig.
7).
Cross not rectangular; the two anterior angles smaller than the two
posterior. All four arms club-shaped, twice as broad at their rounded
obtuse distal end as at their base, of unequal length. Posterior principal
arm one and a fourth times as long as the posterior, and one and two-thirds
as long as the lateral arms. Patagium incomplete, enveloping only the basal
half of the arms. I call this species after the great Greek philosopher
Democritus.
_Dimensions._--Radius of the posterior arm 0.3, of the anterior 0.25, of
each lateral arm 0.22; basal breadth 0.05, distal breadth 0.1.
_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.
Genus 237. _Stephanastrum_,[276] Ehrenberg, 1847, Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, p. 54.
_Definition._--#Porodiscida# with four simple, undivided, chambered arms,
connected on the distal ends by a spongy, square or rhomboidal, patagial
girdle (or a patagium with four large, interbrachial openings). Shell
either regular or bilateral (with equal or unequal arms).
{549}The genus _Stephanastrum_, founded (1847) by Ehrenberg for the very
peculiar _Stephanastrum rhombus_, differs from the nearly allied foregoing
genera in the imperfect development of the peculiar patagium, connecting
only the distal ends of the four arms, while it is absent at their base.
Two new species, different from _Stephanastrum rhombus_ by the regular
square form, were found in the Challenger collection.
Subgenus 1. _Stephanastrella_, Haeckel.
_Definition._--All four arms of the cross have the same size.
1. _Stephanastrum quadratum_, n. sp. (Pl. 46, fig. 5).
All four arms of the same size, six times as long as broad at their base,
ending with a strong, short, four-sided pyramidal spine. In the outer half
of each arm are two opposite lateral spongy wings, which form an
equilateral triangle, and from union of the bases of the four triangles
arises the peculiar patagium, which forms a square with four large
interbrachial openings.
_Dimensions._--Radius of each arm 0.25, basal breadth 0.035; length of the
sides of the square patagium 0.3.
_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.
2. _Stephanastrum capitatum,_ n. sp. (Pl. 44, fig. 1).
All four arms of the same size, five times as long as broad at their base,
at their distal end with a spongy, nearly spherical capitulum of twice
their breadth, provided with a very strong, angular, pyramidal, terminal
spine (half as long as the arm). All four arms connected by a square
patagium, arising immediately below the capitula, and perforated by four
large interbrachial openings.
_Dimensions._--Radius of each arm (without the terminal spine) 0.25, basal
breadth 0.05; length of the sides of the square patagium 0.3.
_Habitat._--Pacific, central area. Station 265, depth 2900 fathoms.
Subgenus 2. _Stephanastromma_, Haeckel.
_Definition._--Two opposite arms of the cross larger than the two others.
3. _Stephanastrum rhombus,_ Ehrenberg.
_Stephanastrum rhombus_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig.
33; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxv. fig. 1.
Two arms of the longitudinal axis one and a third times as long as two arms
of the transverse axis. All four arms linear, about eight times as long as
broad, at their distal end somewhat {550}thickened, club-shaped, with a
pyramidal terminal spine. The ends of the arms are connected by a
riband-shaped, straight, spongy patagium of the same breadth as the arms.
Between the rhomboidal patagium and the arms remain four large rectangular
triangles as interbrachial openings.
_Dimensions._--Radius of the longer arms 0.2, of the shorter 0.15; basal
breadth 0.02; length of the sides of the rhombic patagium 0.25.
_Habitat._--Fossil in the rocks of Barbados.
Genus 238. _Dicranastrum_,[277] Haeckel, 1881, Prodromus, p. 460.
_Definition._--#Porodiscida# with four forked, spongy, or chambered arms,
without a patagium; shell regular (not bilateral), with four equal arms
crossed at right angles.
The genus _Dicranastrum_ comprises a number of very remarkable, hitherto
unknown, Euchitonida, which are rather common in the Pacific (mainly on the
surface), and characterised by the bifurcation of the cross-arms of the
regular square shell. It bears therefore to its probable ancestral form,
_Stauralastrum_, the same relation that in the triradiate Euchitonida
_Chitonastrum_ does to _Dictyastrum_. The arms are commonly of very
delicate structure, more or less spongy.
Subgenus 1. _Dicranaster_, Haeckel.
_Definition._--Each cross-arm with two simple branches.
1. _Dicranastrum furcatum_, n. sp. (Pl. 47, fig. 2).
Arms simply forked, three times as long as broad at their base, with eight
blunt ends of the fork-branches. The simple proximal half of each arm about
the same size as each branch of the dichotomous distal part, twice as long
as broad. Edges of the arms ragged.
_Dimensions._--Radius of each arm 0.38, basal breadth 0.12; breadth of the
forked part 0.3.
_Habitat._--Pacific, central area, Station 271, surface.
2. _Dicranastrum dichotomum_, n. sp.
Arms simply forked, four times as long as broad at their base; each arm
with two blunt branches. The simple proximal part of each arm is three
times as long and twice as broad as each branch of the dichotomous distal
part. Ends of the arms blunt, truncated.
_Dimensions._--Radius of each arm 0.35, basal breadth 0.08; breadth of the
forked part 0.2.
_Habitat._--South Pacific, Station 281, surface.
{551}3. _Dicranastrum cornutum_, n. sp. (Pl. 45, fig. 2).
_Hagiastrum cornutum_, Haeckel, 1879, Atlas (pl. xlv. fig. 2).
Four arms simply forked, four times as long as broad; each arm with two
triangular diverging branches ending in strong conical spines. The simple
basal part of each arm about of the same length as each branch of the
distal part, twice as long as broad. Distance between the terminal spines
of each arm nearly as great as its length.
_Dimensions._--Radius of the arm 0.24, basal breadth 0.05; breadth across
the bifurcation 0.12.
_Habitat._--South Atlantic, Station 325, surface.
4. _Dicranastrum antilope_, n. sp.
Four arms simply forked, three times as long as broad; each arm with two
lanceolate diverging branches, ending in strong angular spines. The simple
basal part of each arm is twice as long as each branch of the distal part.
Distance of the two terminal spines of each arm scarcely half as great as
its length.
_Dimensions._--Radius of the arm 0.32, basal breadth 0.11; breadth of the
branches 0.07.
_Habitat._--Tropical Atlantic (off Ascension), Station 342, surface.
Subgenus 2. _Tricranastrum_, Haeckel, 1881, Prodromus, p. 460.
_Definition._--Each cross arm with three terminal branches, one middle
(perradial) and two lateral (adradial) branches.
5. _Dicranastrum wyvillei_, n. sp. (Pl. 47, fig. 3).
_Tricranastrum wyvillei_, Haeckel, 1879, Natürl. Schöpfungsgesch., p.
705, Taf. xvi. fig. 5.
Arms trifid, one and a half times as long as broad; each arm with three
blunt terminal branches of equal size. The simple basal part of each arm
twice as long as the trifid distal part. (The central capsule depicted in
fig. 3, Pl. 47, has the same form as the skeleton, and is only a little
smaller.)
_Dimensions._--Radius of the arm 0.4, basal breadth 0.12, greatest breadth
(in the distal part) 0.24.
_Habitat._--Pacific, central area, Station 271, surface.
6. _Dicranastrum tricuspis_, n. sp.
Arms trifid, twice as long as broad; each arm with three pointed terminal
branches, ending in strong conical spines, the middle branch somewhat
larger than the other two. The simple basal part of each arm three times as
long as the trifid distal part.
_Dimensions._--Radius of the arm 0.3, basal breadth 0.06, greatest breadth
(in their distal part) 0.15.
_Habitat._--North Pacific, Station 244, surface.
{552}7. _Dicranastrum trifarium_, n. sp.
Arms trifid, three times as long as broad at their base; each arm with
three pointed terminal branches, ending in strong sulcate spines; the
middle branch twice as large as the two others. The simple basal part of
each arm two and a half times as long as the trifid distal part.
_Dimensions._--Radius of the arm 0.35, basal breadth 0.03, greatest breadth
(in the distal part) 0.05.
_Habitat._--South Pacific, Station 298, surface.
Subgenus 3. _Tetracranastrum_, Haeckel.
_Definition._--Each cross-arm with four terminal branches, the two
fork-branches being again bifurcated.
8. _Dicranastrum bifurcatum_, n. sp. (Pl. 47, figs. 1, 1_a_).
Arms doubly forked or quadripartite, six times as long as broad at their
base; each arm in its proximal half simple, three times as long as broad;
in its distal half doubly forked; the secondary branches with blunt,
roundish ends, nearly as large as the primary branches. Central disk (fig.
1_a_) with three concentric rings around the central chamber; from its
periphery radiate thin radial beams in the spongy framework of the delicate
arms. The central capsule has the same form as the skeleton, and is only a
little smaller.
_Dimensions._--Radius of the arm 0.45, basal breadth 0.08; breadth of the
terminal branches 0.03.
_Habitat._--North Pacific, east of Japan, Station 241, surface.
Genus 239. _Myelastrum_,[278] Haeckel, 1881, Prodromus, p. 460.
_Definition._--#Porodiscida# with four forked, spongy, or chambered arms,
without a patagium; shell bilateral, with paired different arms; two equal
anterior arms of different shape from the two equal posterior arms.
The genus _Myelastrum_ differs from the foregoing _Dicranastrum_, the
ancestral form, by the twofold differentiation of the four arms. Whilst in
the latter all four arms are equal, separated by equal angles, here the two
anterior arms are constantly different from the two posterior. The lateral
angles between the two arm-pairs are equal, while the posterior and the
anterior angle (between the two arms of each pair) are more or less
different. The shell assumes, therefore, a very characteristic bilateral
form, similar to the "quadricorn cross" of the grey central substance in
the transverse section of the human medulla spinalis. Though the spongy
shell is commonly a most delicate and {553}thin disk it nevertheless
reaches unusual dimensions, its diameter in some species being more than a
millimetre.
Subgenus 1. _Myelastrella_, Haeckel.
_Definition._--Posterior arms simple, undivided; anterior arms lobated or
cleft, with one or more incisions at the distal end.
1. _Myelastrum medullare_, n. sp. (Pl. 47, fig. 13).
Anterior arms bifid, nearly square, with a shallow incision at their broad
truncated end. Posterior arms somewhat smaller, nearly triangular, with
simple blunt ends. Sagittal constriction three-fourths as large as the
transverse one. Surface smooth.
_Dimensions._--Radius of the anterior arms 0.36, of the posterior 0.3;
longitudinal constriction 0.24, transverse 0.36.
_Habitat._--Pacific, central area, Station 271, surface.
2. _Myelastrum spinale_, n. sp.
Anterior arms bifid, twice as long as broad, with a deep incision at their
truncated end. Posterior arms slender, half as large, with simple blunt
ends. Sagittal constriction one and a half times as large as the
transverse. Surface spiny.
_Dimensions._--Radius of the anterior arms 0.4, of the posterior 0.2;
longitudinal constriction 0.3, transverse 0.2.
_Habitat._--North Pacific, Station 248, surface.
3. _Myelastrum heteropterum_, n. sp. (Pl. 47, fig. 8).
Anterior arms trifid, about as long as broad, with two incisions at their
broad truncated end. Posterior arms about half as large, simple, with
rounded blunt ends. Sagittal constriction two-thirds as large as the
transverse. Surface bristly.
_Dimensions._--Radius of the anterior arms 0.65, of the posterior 0.035;
longitudinal constriction 0.4, transverse 0.6.
_Habitat._--South Pacific, Station 291, surface.
Subgenus 2. _Myelastromma_, Haeckel.
_Definition._--All four arms (posterior as well as anterior) lobated or
cleft.
4. _Myelastrum octocorne_, n. sp. (Pl. 47, fig. 12).
All four arms with a deep incision in their distal half; anterior arms
broader, but shorter than the posterior; in the anterior arms the two lobes
are of the same size, in the posterior arms the {554}median lobe is longer
than the lateral lobe. Sagittal constriction little smaller than the
transverse. Surface of the disk rough.
_Dimensions._--Radius of the anterior arms 0.45, of the posterior 0.62;
longitudinal constriction 0.25, transverse 0.3.
_Habitat._--Pacific, central area, Station 271, surface.
5. _Myelastrum farfalla_, n. sp. (Pl. 47, fig. 10).
All four arms with a shallow incision at their distal end. Anterior arms
broader, but shorter than the posterior; in each arm the anterior lobe is
shorter than the posterior. Sagittal constriction smaller than the
transverse. Surface smooth.
_Dimensions._--Radius of the anterior arms 0.4, of the posterior 0.6;
longitudinal constriction 0.5, transversal stricture 0.6.
_Habitat._--Pacific, central area, Station 274, surface.
6. _Myelastrum papilio_, n. sp. (Pl. 47, fig. 6).
All four arms with a shallow incision at their distal end. Anterior arms
triangular, of the same breadth, but of the double length of the square
posterior arms. Sagittal and transverse constrictions of the same length.
Surface ciliated. (Resembles a butterfly.)
_Dimensions._--Radius of the anterior arms 0.7, of the posterior 0.4;
longitudinal and transverse constrictions 0.4.
_Habitat._--North Pacific, near Japan, Station 241, surface.
7. _Myelastrum decaceros_, n. sp. (Pl. 47, fig. 7).
Anterior arms bifid, with one shallow incision at their distal end.
Posterior arms of the same length, but much broader, trifid, with two
incisions (one larger and one smaller). Sagittal and transverse
constrictions of the same length. Surface spiny.
_Dimensions._--Radius of all four arms 0.4; longitudinal and transverse
constrictions 0.35.
_Habitat._--Pacific, central area, Station 272, surface.
8. _Myelastrum dodecaceros_, n. sp. (Pl. 47, figs. 11, 11_a_).
Anterior arms trifid, with two shallow incisions at their distal end.
Posterior arms about one-third larger, also trifid, with one deeper
anterior and one shallower posterior incision. Sagittal constriction much
longer than the transverse. Surface ciliated, covered with numerous thin
and long radial bristles (fig. 11_a_).
_Dimensions._--Radius of the anterior arms 0.5, of the posterior 0.7;
longitudinal constriction 0.5, transverse 0.35.
_Habitat._--Pacific, central area, Station 270, surface.
{555}9. _Myelastrum ciliatum_, n. sp.
Anterior arms trifid, with two shallow incisions. Posterior arms somewhat
smaller, also trifid, with two deeper incisions. Sagittal constriction a
little larger than the transverse. Margin of the disk ciliated, with radial
bristle-shaped spines, as prolongations of the inner radial beams, arising
from the central disk.
_Dimensions._--Radius of the anterior arms 0.6, of the posterior 0.5;
longitudinal constriction 0.4, transverse 0.35.
_Habitat._--South Pacific, Station 288, surface.
10. _Myelastrum lobatum_, n. sp.
Anterior arms somewhat broader but shorter than the posterior arms. Each
arm four-lobed, with three terminal shallow incisions of nearly equal size.
Sagittal constriction smaller than the transverse. Surface of the disk
bristly.
_Dimensions._--Radius of the anterior arms 0.4, of the posterior 0.5;
longitudinal constriction 0.3, transverse 0.35.
_Habitat._--North Pacific, Station 253, surface.
11. _Myelastrum rotula_, n. sp.
Anterior arms little broader than the posterior, but of the same length.
Each arm four-lobed, with three terminal deep incisions of equal size.
Sagittal and transverse constrictions equal. The whole disk nearly
circular, resembles a wheel with sixteen spokes. Surface smooth.
_Dimensions._--Radius of all four arms 0.5; longitudinal and transverse
constrictions 0.3.
_Habitat._--Pacific, central area, Station 274, surface.
12. _Myelastrum giganteum_, n. sp.
Anterior arms somewhat broader and shorter than the posterior. Each arm
four-lobed, with three shallow terminal incisions, the middle incision
twice as deep as the two laterals. Sagittal constriction a little larger
than the transverse. Margin ciliated, with radial bristle-shaped spines as
prolongations of the inner radial beams, proceeding from the central disk
(as in _Myelastrum dodecaceros_, Pl. 47, figs. 11, 11_a_).
_Dimensions._--Radius of the anterior arms 0.6, of the posterior 0.8;
longitudinal constriction 0.6, transverse 0.5.
_Habitat._--Pacific, central area, Station 271, surface.
{556}13. _Myelastrum anomalum_, n. sp. (Pl. 47, fig. 9).
All four arms of different size and form; anterior arms broader, posterior
longer; one anterior arm trifid, the three other arms bifid; length of the
branches unequal; all four angles between the arms unequal. (This anomalous
form, seen only once, may be an individual abnormality.)
_Dimensions._--Radius of the arms 0.4 to 0.7; constrictions 0.3.
_Habitat._--North Pacific, Station 237, surface.
Genus 240. _Pentalastrum_,[279] Haeckel, 1881, Prodromus, p. 461.
_Definition._--#Porodiscida# with five simple, undivided, chambered arms,
without a patagium.
The genus _Pentalastrum_ opens the small series of Euchitonida, in which
the shell is not provided with three or four arms, as usual, but with five.
All forms of this little group are rare. Some species resemble in their
external form and in the articulation of their arms certain forms of
Asterida. In _Pentalastrum_, the most simple genus, the five arms are
simple, not forked, and without a patagium. It can be derived from
_Dictyastrum_ or _Stauralastrum_ by increase of the number of arms.
Subgenus 1. _Pentalastrella_, Haeckel.
_Definition._--All five arms equal, with equal angles between them. Shell a
regular pentagon.
1. _Pentalastrum asteracanthion_, n. sp.
All five arms equal, club-shaped, at their thickened obtuse end three times
as broad as at their base, twice as long as broad. Angles between the arms
equal.
_Dimensions._--Radius of each arm 0.2, basal breadth 0.03, distal breadth
0.08.
_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.
2. _Pentalastrum astropecten_, n. sp.
All five arms equal, with five to six distinct, simple joints, the basal
joint two-thirds as broad as the terminal joint, which bears a strong
conical spine. Angles between the arms equal. (Resembles _Pentinastrum
asteriscus_, Pl. 44, fig. 2, but has no patagium.)
_Dimensions._--Radius of each arm 0.14, basal breadth 0.024, distal breadth
0.036.
_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.
{557}Subgenus 2. _Pentalastromma_, Haeckel.
_Definition._--Arms of different sizes, one odd arm larger than the two
others; the opposite odd angle generally different from the four other
angles.
3. _Pentalastrum ophidiaster_, n. sp. (Pl. 44, fig. 3).
Arms nearly triangular, at their obtuse truncated distal end twice as broad
as at their base. Four arms equal, with five joints each; the fifth arm
twice as long, with seven joints. Angles between the arms nearly equal; the
odd angle a little larger.
_Dimensions._--Radius of the larger odd arm 0.25, of the four smaller arms
0.15; basal breadth 0.035, distal breadth 0.07.
_Habitat._--Pacific, central area, Station 274, surface.
4. _Pentalastrum cometa_, n. sp.
Arms nearly cylindrical, at their obtuse truncated distal end one and a
half times as broad as at their base. Posterior odd arm very large, with
eleven joints, about three times as long as the two lateral arms (with five
joints each) and four times as long as the two anterior arms (with three
joints each). Angles between the paired arms different; the two lateral
angles smaller than the two posterior, and these smaller than the odd
anterior angle.
_Dimensions._--Radius of the odd posterior arm 0.5, of the lateral arms
0.25, of the anterior arms 0.18; basal breadth 0.05, distal breadth 0.08.
_Habitat._--South Pacific, Station 288, surface.
Genus 241. _Pentinastrum_,[280] Haeckel, 1881, Prodromus, p. 461.
_Definition._--#Porodiscida# with five simple, undivided, chambered arms,
connected by a patagium.
The genus _Pentinastrum_ differs from the foregoing _Pentalastrum_ only in
the development of a patagium or connecticulum between the arms, and bears
therefore the same relation to it that _Histiastrum_ does to
_Stauralastrum_, or _Hymeniastrum_ to _Dictyastrum_.
1. _Pentinastrum asteriscus_ , n. sp. (Pl. 44, fig. 2).
All arms equal, twice as long as broad, at their base two-thirds as broad
as at their truncated distal end, which bears a strong, pyramidal, terminal
spine. Each arm is divided by five transverse septa into six joints or
chambers, and each of these by a radial beam into a pair of chambers. The
five radial beams arise from the innermost chamber of the central disk, and
end in the five terminal {558}spines. The diameter of the central disk is
larger than the length of the arms. The angles between the arms are equal
and filled up by an incomplete patagium, so that the whole disk forms a
regular pentagon with five concave sides.
_Dimensions._--Radius of each arm (without terminal spine) 0.14; breadth at
their base 0.02, at their terminal joint 0.03; radius of the central disk
0.06.
_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.
2. _Pentinastrum goniaster_, n. sp.
? _Stephanastrum_ sp., Bury, 1862, Polycystins of Barbados, pl. xx. fig.
1.
All five arms equal, four times as long as broad, club-shaped, at their
globose distal end twice as broad as at their base, and armed with a strong
conical terminal spine. Diameter of the central disk equals only one-third
of the length of the arms. The articulation of the spongy arms is somewhat
obscure. Patagium complete, totally fills up the interbrachial spaces, so
that the whole disk forms a regular pentagon with five rectilinear sides,
except that the terminal spines project at the corners.
_Dimensions._--Radius of each arm 0.18, basal breadth 0.02, distal breadth
0.04; radius of the central disk 0.05.
_Habitat._--South Pacific, Station 295, depth 1500 fathoms; also fossil in
the rocks of Barbados.
Genus 242. _Pentophiastrum_,[281] n. gen.
_Definition._--#Porodiscida# with five forked chambered arms, without a
patagium.
The genus _Pentophiastrum_ differs from the two preceding genera by the
bifurcation of the five arms, and can be derived either from _Pentalastrum_
by the ramification of the distal ends of the arms, or from the similar
_Myelastrum_ by the increase in the number of arms.
1. _Pentophiastrum dicranastrum_, n. sp.
All five arms equal, with equal angles between them. Each arm in the basal
half simple, in the distal half forked; both branches of it equal, with
obtuse ends. (This regular species resembles _Dicranastrum furcatum_, Pl.
47, fig. 2, but with five rays instead of four; also the form of the arms
is more slender and the edges smooth.)
_Dimensions._--Radius of each arm 0.25, breadth 0.05.
_Habitat._--Equatorial Atlantic, Station 347, depth 2250 fathoms.
Subgenus _Pentophiastromma_, Haeckel.
_Definition._--Arms of different size, one odd arm opposite to the angle
between both arm-pairs.
{559}2. _Pentophiastrum caudatum_, n. sp. (Pl. 47, fig. 5).
Arms in pairs different; four arms in the basal half simple, in the distal
half forked; the fifth (posterior) odd arm simple, undivided, cylindrical;
the anterior pair a little smaller than the posterior; the neighboring
branches of the two pairs on each side larger than the two others. Axes of
the arms and their branches straight.
_Dimensions._--Radius of the arms about 0.5, breadth 0.12.
_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.
3. _Pentophiastrum forcipatum_, n. sp. (Pl. 47, fig. 4).
Arms in pairs different, all in the basal two thirds simple, in the distal
third forked. Only in the posterior (odd) arm both branches are equal, in
the four others unequal. The common axis of the posterior lateral pair is
horizontal, perpendicular to the median line; the axes of the anterior pair
are pincer-like, concavely curved towards the median line or principal
axis.
_Dimensions._--Radius of the arms about 0.5, breadth 0.14.
_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.
Genus 243. _Hexalastrum_,[282] Haeckel, 1881, Prodromus, p. 461.
_Definition._--#Porodiscida# with six simple chambered arms, without a
patagium.
The genus _Hexalastrum_, together with the following _Hexinastrum_,
encloses those _Euchitonida_ in which the number of the chambered arms
surrounding the central disk amounts to six. This is the highest number of
these articulated marginal appendages which is reached in any #Discoidea#.
Formerly (1881) in my Prodromus, p. 459, I supposed that the same number
was reached also by one Coccodiscid, and called this genus _Hexactura_.
Afterwards I was convinced that this form was also a _Hexalastrum_.
1. _Hexalastrum palmanthum_, n. sp.
All six arms equal, with equal angles between them. Each arm club-shaped,
three times as long as broad, twice as broad at the thickened distal end as
at the base, without a terminal spine.
_Dimensions._--Radius of each arm 0.2, basal breadth 0.02, distal breadth
0.06.
_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.
2. _Hexalastrum crinanthum_, n. sp.
All six arms equal, with equal angles between them. Each arm club-shaped,
four times as long as broad, at the egg-shaped distal end three times as
broad as in the linear basal part, provided {560}with numerous short
conical spines and one longer terminal spine. (Resembles _Stauralastrum
rhopalophorum_, Pl. 45, fig. 1, but with six rays instead of four.)
_Dimensions._--Radius of each arm 0.3, basal breadth 0.03, distal breadth
0.08.
_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.
Subgenus _Hexalastromma_, Haeckel.
_Definition._--Arms more or less different in size or form; shell
bilateral.
3. _Hexalastrum orchidaceum_, n. sp. (Pl. 44, fig. 5).
_Hexactura orchidacea_, Haeckel, 1881, Prodromus, p. 459.
Arms different in length, so that two unequal opposite odd arms determine
the main axis, and the four other arms lie on both sides of this as two
different pairs. The proportion of their relative length is the
following:--anterior lateral arms five, anterior odd arm six; posterior
lateral arms seven, posterior odd arm eight. Each arm is club-shaped, two
to three times as long as broad, and divided into six to eight joints by
five to seven transverse septa; its distal end is armed with a terminal
spine and twice as broad as its base.
_Dimensions._--Radius of the posterior odd arm 0.4, of the anterior odd arm
0.3; of the posterior lateral pair 0.35, of the anterior lateral pair 0.25;
basal breadth 0.08, distal breadth 0.16.
_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.
Genus 244. _Hexinastrum_,[283] Haeckel, 1881, Prodromus, p. 461.
_Definition._--#Porodiscida# with six simple, undivided, chambered arms,
connected by a patagium.
The genus _Hexinastrum_ differs from its ancestral form _Hexalastrum_ by
the development of a patagium between the arms. The only observed species
is regular.
1. _Hexinastrum geryonidum_, n. sp. (Pl. 44, fig. 4).
_Hexalastrum geryonidum_, Haeckel, 1879, Atlas (pl. xliv. fig. 4).
Disk quite regular with six radii; all six arms of the same size and form,
at their broad, convexly rounded, smooth end five times as broad as at
their narrow base, and little longer than broad. Each arm is divided by
eight transverse septa into nine simple joints or chambers of the same
height; the breadth of the distal chambers increases rapidly. The regular,
hexagonal, central disk exhibits four concentric rings around the central
chamber. Patagium between the arms incomplete, with concavely fluted edge.
_Dimensions._--Radius of each arm 0.15, basal breadth 0.016, distal breadth
0.08; radius of the central disk 0.04.
_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.
{561}Family XXII. #PYLODISCIDA#, n. fam. (Pl. 48, figs. 12-20).
_Definition._--#Discoidea# without phacoid shell, with flat discoidal
shell, in which a simple spherical central chamber is surrounded by one or
two concentric triradial girdles; each girdle with three gates, separated
by three simple arm-chambers. Surface of the disk with three open or
latticed gates on each flat side.
The family #Pylodiscida# represents a new small but interesting group of
#Discoidea#, which exhibits rather complex affinities to different groups
of #Sphærellaria#. In my Prodromus (1881, p. 464) I had enumerated only two
genera of this family, _Triopyle_ and _Hexapyle_, and had united them with
_Tetrapyle_ and allied genera in the family Pylonida. Indeed, the
resemblance of skeletal structure in the two groups is very great. The most
simple forms of both groups exhibit a simple spherical latticed central
chamber, which is surrounded by few latticed chambers of similar size and
form, separated by open gates. But in the Pylonida these chambers are
opposite in pairs, and form together a complete lattice-girdle around the
central chamber, whereas in the Pylodiscida the chambers are not opposite
in pairs in one axis, and form therefore only latticed half girdles, which
arise from the central chamber like radial arms, and may perhaps better be
called "arm-chambers"; their number is constantly three. The free open
spaces between these three arm-chambers form three gates, comparable to the
two or four gates of _Amphipyle_, _Tetrapyle_, &c., and become afterwards
closed by lattice-work in a similar way in both groups. A more important
difference between them is indicated by the further mode of growth. The
Pylonida build new girdles in all three dimensive planes (alternating in
the transverse, lateral and sagittal planes); their geometric fundamental
form is therefore the "lentellipsis" or the "triaxial ellipsoid." The
Pylodiscida, however, grow only at the periphery of the discoidal shell in
one single plane (the equatorial plane); their fundamental form is
therefore the biconvex lens or the flat disk (a shortened cylinder). This
important difference is my deciding motive, in separating the latter from
the former and in regarding the Pylodiscida as true #Discoidea#, the more
so as they can easily be derived from _Archidiscus_, the fundamental and
ancestral form of the Porodiscida.
One single form of _Archidiscus_ seems to be of peculiar importance in this
relation, viz., _Archidiscus hexoniscus_ (Pl. 48, fig. 10). In this species
the simple central chamber is surrounded by a latticed ring or girdle,
composed of six equal chambers of the same size and form, all lying in the
same plane with the central chamber. In a nearly allied species, viz.,
_Archidiscus pyloniscus_, the six ring-chambers are different, three
smaller (with denser network) alternating with three larger (of looser
network); if we imagine the network of the latter reduced to a marginal bar
we get _Triopyle_, and if also this bar disappear by reduction we get
_Triolena_, the most simple form of the Pylodiscida. {562}Even _Archidiscus
pyloniscus_ may possibly represent the same form among the Porodiscida as
_Triodiscus lenticula_ among the Pylodiscida; this important form indicates
clearly the close affinity of the two families.
If we take the latter, nearly identical form as the common starting point
of both families of Cyclodiscaria, then probably _Triopyle_ and _Triolene_
must be regarded as retrograde forms, derived from _Triodiscus_ in the one
case, from _Archidiscus_ in the other, by reduction of three interradial
arm-chambers, whilst three perradial only remain. But it is also possible
that the most simple form, _Triolene_, originated independently from some
_Cenosphæra_, three simple radial chambers, like the latticed central
chamber, being derived from the latter by apposition in three equidistant
radii, whilst three other radii between them remained free. In this case
the other genera of Pylodiscida are derived from their ancestral form
_Triolene_.
Adopting this latter view, we find that all eight genera of Pylodiscida,
here distinguished, may be regarded as following members of a continuous
series. If the three simple arm-chambers of _Triolene_, surrounding the
equal central chamber, become united at their distal ends by a concentric
equatorial ring, then originates _Triopyle_; and this graduates into
_Triodiscus_ by fenestration of the three open gates between the three
latticed arms. Whilst these three genera form together the subfamily
Triopylida, a second family, Hexapylida, is composed of three other
analogous genera, in which the same process of development becomes
repeated.
_Pylolena_, the most simple form of Hexapylida, arises from _Triodiscus_ by
the development of three new arm-chambers (of the second order) which are
apposed at the distal end of the three primary arm-chambers (of the first
order) in the same radius. If the distal ends of these three secondary
arm-chambers become united by a concentric latticed ring or girdle, we get
_Hexapyle_ (with six open gates, two in each radius), and if its six gates
become afterwards closed by loose lattice-work, we arrive at _Pylodiscus_
(a repetition of _Triodiscus_).
A third subfamily, Discopylida, is formed by the building of a chambered
equatorial girdle around the margin of _Pylodiscus_. This girdle has quite
the same structure as the similar chambered rings or girdles of the
Porodiscida and Coccodiscida. Between the two sieve-plates of the disk
surface is enclosed a variable number (twelve to twenty-four or more) of
chambers, imperfectly separated by radial beams, which connect the margin
of the _Pylodiscus_-shell with an outer peripheral concentric ring. In
_Discozonium_ this marginal ring is perfect, whilst in _Discopyle_ it is
interrupted by a peculiar large opening, a "marginal osculum" surrounded by
a corona of spines, quite the same remarkable formation which we
encountered in _Ommatodiscus_ among the Porodiscida.
All Pylodiscida are therefore triradial (with three perradial arms and
three interradial gates between them), and many of them have a great
resemblance to certain triradial Porodiscida and Spongodiscida, perhaps not
only a morphological resemblance, but also {563}a true phylogenetic
relation. But it is remarkable that we do not find further forms of
development in this family, by multiplication either of the arm-chambers
(further growth in the three perradii) or of the concentric chambered rings
(in the periphery of the disk margin).
The central capsule of the Pylodiscida is constantly flat, discoidal, and
enclosed between the two sieve-plates of the surface. Its form is either
circular or triangular.
_Synopsis of the Genera of the Pylodiscida._
-------------------------------------------------------------------------
I. Subfamily Triopylida.
Three gates between three simple arm-chambers.
-----------------------------------------------------------------------
Three gates open, without a barring equatorial
girdle, 245. _Triolena_.
Three gates barred by a { Gate-faces simple, 246. _Triopyle_.
latticed equatorial {
girdle. { Gate-faces latticed, 247. _Triodiscus_.
-------------------------------------------------------------------------
II. Subfamily Hexapylida.
Six gates between three double arm-chambers (three inner and three
outer); no chambered marginal girdle.
-------------------------------------------------------------------------
Three outer gates open, without a barring equatorial
girdle, 248. _Pylolena_.
{ Both faces of the outer
Three outer gates barred { gates simple, 249. _Hexapyle_.
by a latticed (second) {
equatorial girdle. { Both faces of the outer
{ gates latticed, 250. _Pylodiscus_.
-------------------------------------------------------------------------
III. Subfamily Discopylida.
Six gates between three double arm-chambers.
------------------------------------------------------------------------
{ No peculiar osculum on
In the equatorial plane { the margin of the disc, 251. _Discozonium_.
on the margin of the {
Pylodiscus-shell is a { One pecuiar osculum (with
chambered equatorial { a corona of spines) on
girdle. { the margin of the disc, 252. _Discopyle_.
Subfamily 1. TRIOPYLIDA, Haeckel.
_Definition._--#Pylodiscida# with a simple, spherical or lenticular,
central chamber, surrounded by three simple arm-chambers, which are
separated by three notches or gates.
Genus 245. _Triolena_,[284] n. gen.
_Definition._--#Pylodiscida# with a simple, spherical or lenticular,
central chamber, surrounded by three simple arm-chambers. Notches between
the three arms open.
The genus _Triolena_ is the most simple form of all Pylodiscida, and must
be regarded as their common ancestral form, from an ontogenetic as well as
a phylogenetic point of view. The small shell is composed of a simple,
spherical or lenticular, latticed, central chamber, and of three simple,
surrounding equal arms, which are also simple latticed chambers, lie in the
equatorial plane, and are separated by three equal angles or open gates.
{564}1. _Triolena primordialis_, n. sp. (Pl. 48, fig. 12).
Arm-chambers trapezoid, nearly square, of the same size as the circular,
lenticular, primordial, central chamber. Surface of the disk smooth.
_Dimensions._--Diameter of the shell 0.045, of the central chamber 0.015,
of each arm 0.015.
_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.
2. _Triolena tribelone_, n. sp.
Arm-chambers lanceolate, of the same breadth as and twice the length of the
triangular, central chamber; at the pointed end of each arm is a conical
terminal spine (in the equatorial plane). Surface of the disk thorny.
_Dimensions._--Diameter of the shell 0.05, of the central chamber 0.015;
length of the arms 0.02, breadth 0.016.
_Habitat._--North Pacific, Station 244, depth 2900 fathoms.
3. _Triolena trispinosa_, n. sp.
Arm-chambers ovate, in the basal half nearly as broad as the hexagonal
central chamber, at the pointed distal end with a strong conical radial
spine of double the length. Surface rough.
_Dimensions._--Diameter of the shell 0.055, of the central chamber 0.02.
_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.
4. _Triolena hexabelone_, n. sp.
Arm-chambers nearly triangular, at the base half as broad as the hexagonal
central chamber, at the truncate distal end one and a half times as broad,
and armed with two radial conical spines (in the equatorial plane). Surface
of the disk smooth.
_Dimensions._--Diameter of the shell 0.06, of the central chamber 0.02.
_Habitat._--South Pacific, Station 295, depth 1500 fathoms.
5. _Triolena trigonalis_, n. sp.
Arm-chambers nearly triangular, at the base half as broad as the circular
central chamber, at the concave lunulate distal end twice as broad, and
armed with four conical radial spines (two on each side of the equatorial
plane). Surface thorny.
_Dimensions._--Diameter of the shell 0.05, of the central chamber 0.015.
_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.
{565}Genus 246. _Triopyle_,[285] Haeckel, 1881, Prodromus, p. 464.
_Definition._--#Pylodiscida# with a simple, spherical or lenticular,
central chamber, surrounded by three simple arm-chambers. Notches between
the three arms transformed into gates by a connecting equatorial girdle.
The genus _Triopyle_ differs from the preceding _Triolene_ in the
development of a simple ring or latticed equatorial girdle, which connects
the distal ends of the three arm-chambers, and transforms the open notches
between them into three gates. The ring may be circular, triangular, or
hexagonal.
1. _Triopyle circulus_, n. sp.
Disk circular, three times as broad as the hexagonal central chamber. Three
arm-chambers trapezoidal, at the convex distal end as broad, at the base
half as broad as the three circular gates between them. Surface smooth. No
marginal spines on the girdle.
_Dimensions._--Diameter of the disk 0.045, of the gates 0.015.
_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.
2. _Triopyle hexagona_, n. sp. (Pl. 48, fig. 13).
Disk hexagonal, three times as broad as the circular central chamber. Three
arm-chambers trapezoidal, at the truncated distal end as broad, at the base
half as broad as the three triangular gates between them. Surface smooth.
No marginal spines.
_Dimensions._--Diameter of the disk 0.05, of the gates 0.02.
_Habitat._--North Pacific, Station 244, depth 2900 fathoms.
3. _Triopyle trigona_, n. sp.
Disk triangular, four times as broad as the circular central chamber. Three
arm-chambers nearly triangular, at the narrow base half as broad, at the
distal end twice as broad as the circular or roundish gates. Surface
smooth. On the margin (in the equatorial plane) three strong pyramidal
spines (at the end of the arms).
_Dimensions._--Diameter of the disk 0.04, of the gates 0.015.
_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.
4. _Triopyle cordigera_, n. sp.
Disk hexagonal, four times as broad as the hexagonal central chamber. Three
arm-chambers triangular, at the base half as broad as at the truncated
distal end, about the same size as the {566}three heart-shaped gates. On
the six corners of the margin (which forms a regular hexagon) are six
pyramidal radial spines, as prolongations of the arm-edges.
_Dimensions._--Diameter of the disk 0.05, of the gates 0.02.
_Habitat._--Indian Ocean, Ceylon, surface, Haeckel.
5. _Triopyle renigera_, n. sp.
Disk hexagonal, five times as broad as the circular central chamber. Three
arm-chambers trapezoidal, at the base one-third, at the distal end
two-thirds as broad as the three kidney-shaped gates. On the six corners of
the margin (which forms an irregular hexagon) six conical radial spines, as
prolongations of the arm-edges.
_Dimensions._--Diameter of the disk 0.06, of the gates 0.02.
_Habitat._--South Pacific, Station 295, depth 1500 fathoms.
6. _Triopyle spinigera_, n. sp.
Disk roundish, triangular, four times as broad as the triangular central
chamber, which is armed with three radial spines between the arms.
Arm-chambers club-shaped, at the narrow base one-fourth, at the distal end
half as broad as the square gates. On the margin twelve large conical
spines, two opposite on each face of the distal end of each arm-edge. Three
smaller radial spines on the three corners of the girdle (in the same
interradial meridian planes as the three spines of the central chamber).
Compare _Triodiscus spinosus_.
_Dimensions._--Diameter of the disk 0.05, of the gates 0.02.
_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.
Genus 247. _Triodiscus_,[286] n. sp.
_Definition._--#Pylodiscida# with a simple, spherical or lenticular,
central chamber, surrounded by three simple arm-chambers. Notches between
the three arms closed by lattice-work and by an equatorial girdle.
The genus _Triodiscus_ differs from the preceding _Triopyle_ in the
development of loose lattice-work on both sides of the discoidal shell.
This network closes the gates and transforms the whole shell into a
fenestrated lens. The singular species of _Triodiscus_ correspond to
certain species of _Triopyle_.
1. _Triodiscus lenticula_, n. sp.
Disk circular, lenticular, three times as broad as the central chamber.
Three arm-chambers trapezoidal, of the same size and form as the three
gates between them, which are closed by a loose {567}delicate network
(differs from _Triopyle circulus_ by the production of the two convex
latticed plates, which envelop the whole lens). Margin smooth.
_Dimensions._--Diameter of the disk 0.045, of the gates 0.015.
_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.
2. _Triodiscus trigonus_, n. sp.
Disk triangular, four times as broad as the central chamber. Three
arm-chambers at the base half as broad, at the distal end twice as broad as
the roundish gates. Surface smooth. On the three corners of the margin (in
the arm-radius) three strong spines. (Differs from _Triopyle trigona_ only
in the loose framework closing the gates.)
_Dimensions._--Diameter of the disk 0.04, of the gates 0.015.
_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.
3. _Triodiscus spinosus_, n. sp. (Pl. 48, fig. 14).
Disk subcircular, four times as broad as the triangular central chamber.
Three arm-chambers club-shaped, at the base one-third, at the distal end
two-thirds as broad as the semicircular gates. Surface thorny. On the
margin fifteen larger radial spines, three on the corners of the disk (in
the radius of the gates), twelve on the two faces of the arms ends (two
opposite on the edge of each end.) (Differs from _Triopyle spinigera_
mainly by the delicate hexagonal network closing the gates.)
_Dimensions._--Diameter of the disk 0.05, of the gates 0.02.
_Habitat._--North Atlantic, Canary Islands (Lanzerote, Haeckel).
Subfamily 2. HEXAPYLIDA, Haeckel.
_Definition._--#Pylodiscida# with triopyle-shaped medullary shell,
surrounded by three distal arm-chambers, which are separated by three open
notches or gates.
Genus 248. _Pylolena_,[287] n. gen.
_Definition._--#Pylodiscida# with triopyle-shaped medullary shell,
surrounded by three distal arm-chambers. Notches between the three arms
open.
The genus _Pylolena_ opens the series of the Hexapylida, or of those
Pylodiscida in which the centre of the shell is formed by a tri-radiated
medullary shell like _Triopyle_. In the equatorial plane of this
triopyle-shaped disk are developed on its margin three distal arm chambers,
as prolongations of the three arms of _Triopyle_, but much larger. In
_Pylolene_ the three angles or notches between the distal arms remain open,
repeating the form of _Triolene_.
{568}1. _Pylolena inermis_, n. sp.
Arms club-shaped, at the base half as broad, at the rounded distal end as
broad as the triopyle-shaped medullary shell. Surface and margin smooth.
_Dimensions._--Diameter of the cortical shell 0.15, of the medullary shell
0.05.
_Habitat._--Equatorial Atlantic, Station 347, surface; Central Pacific,
Station 272, surface.
2. _Pylolena armata_, n. sp. (Pl. 48, fig. 15).
Arms trapezoid, at the base half as broad, at the distal end twice as broad
as the triopyle-shaped medullary shell. Surface and margin thorny. Twelve
strong conical spines at the distal end of the three arms, two opposite on
both faces of the arm-edges.
_Dimensions._--Diameter of the cortical shell 0.2, of the medullary shell
0.06.
_Habitat._--South Atlantic, Station 325, surface.
Genus 249. _Hexapyle_,[288] Haeckel, 1881, Prodromus, p. 464.
_Definition._--#Pylodiscida# with triopyle-shaped medullary shell,
surrounded by three distal arm-chambers. Notches between the three arms
transformed into gates by a connecting equatorial girdle.
The genus _Hexapyle_ differs from the preceding _Pylolene_ in the
development of an equatorial ring or latticed girdle, which connects the
free extremities of the three distal ends and transforms the open notches
between them into gates. It simulates therefore the formation of
_Triopyle_, from which it differs by duplication of the arm-joints and of
the gates (in each radius occur one proximal and one distal gate).
1. _Hexapyle triangula_, n. sp.
Cortical shell triangular, with three rounded corners, three times as broad
as the triangular triopyle-shaped medullary shell. Surface smooth or rough,
but not spiny. Three arms two-thirds as broad as the three egg-shaped gates
of each side.
_Dimensions._--Diameter of the cortical shell (or length of one side of the
triangle) 0.15, of the medullary shell 0.05; breadth of the gates 0.06, of
the bridges between them 0.04.
_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.
2. _Hexapyle sexangula_, n. sp.
Cortical shell hexagonal, with six equal sides, four times as broad as the
triangular triopyle-shaped medullary shell. Surface rough, but not spiny.
Three arms (on their smallest part) half as broad as the three triangular
gates (on their broadest part).
{569}_Dimensions._--Diameter of the cortical shell 0.16, of the medullary
shell 0.04; breadth of the gates 0.06, of the bridges 0.03.
_Habitat._--North Pacific, Station 244, depth 2900 fathoms.
3. _Hexapyle circularis_, n. sp.
Cortical shell circular, four times as broad as the triangular,
Triopyle-shaped medullary shell. Surface smooth. Three arms half as broad
as the three kidney-shaped gates on each side of the shell.
_Dimensions._--Diameter of the cortical shell 0.2, of the medullary shell
0.05; breadth of the gates 0.08, of the bridges between them 0.04.
_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.
4. _Hexapyle triacantha_, n. sp.
Cortical shell triangular, thorny, with three pointed corners, prolonged
into three strong conical radial spines; its diameter four times as great
as that of the medullary shell. Three arms of the same breadth as the three
egg-shaped gates of each side.
_Dimensions._--Diameter of the cortical shell (or length of one side of the
triangle, without spines) 0.2, of the medullary shell 0.05; breadth of the
gates and of the bridges between them 0.06.
_Habitat._--Indian Ocean, surface; Madagascar, Rabbe.
5. _Hexapyle hexacantha_, n. sp.
Cortical shell hexagonal, thorny, three times as broad as the medullary
shell. Six stronger conical radial spines on the six corners at equal
distances, lying in the equatorial plane of the disk. Three half girdles
half as broad as the three triangular gates of each side.
_Dimensions._--Diameter of the cortical shell 0.15, of the medullary shell
0.05; breadth of the gates 0.05, of the bridges 0.025.
_Habitat._--North Pacific, Station 253, depth 3125 fathoms.
6. _Hexapyle dodecantha_, n. sp. (Pl. 48, fig. 16).
Cortical shell triangular, thorny, with rounded corners, three and a half
times as broad as the medullary shell. Twelve stronger radial spines, six
opposite in pairs on each side of the discoidal shell, as prolongations of
the lateral edges of the triangular gates, which are about the same breadth
as the half girdles between them.
_Dimensions._--Diameter of the cortical shell 0.21, of the medullary shell
0.06; breadth of the gates and of the bridges 0.06.
_Habitat._--Pacific, central area, Station 270, surface.
{570}7. _Hexapyle polyacantha_, n. sp.
Cortical shell circular, thorny, with a circle of numerous conical radial
spines in the periphery; its diameter nearly three times as great as that
of the medullary shell. Three half-girdles half as broad as the three
kidney-shaped gates on each side of the discoidal shell.
_Dimensions._--Diameter of the cortical shell 0.11, of the medullary shell
0.04; breadth of the gates 0.04, of the bridges between them 0.02.
_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.
Genus 250. _Pylodiscus_,[289] n. gen.
_Definition._--#Pylodiscida# with _Triopyle_-shaped medullary shell,
surrounded by three distal arm-chambers. Notches between the three arms
closed by lattice-work and by an equatorial girdle.
The genus _Pylodiscus_ differs from _Hexapyle_ in the development of two
convex plates of lattice-work, which close the six open gates and transform
the disk into a biconvex fenestrated lens. _Pylodiscus_ simulates therefore
the characteristic form of _Triodiscus_; but whilst in the latter we find
only three arm-joints and three simple gates, their number is doubled in
the former.
1. _Pylodiscus triangularis_, n. sp. (Pl. 48, fig. 17).
Cortical shell triangular, with rounded corners, three times as broad as
the triangular, _Triopyle_-shaped medullary shell. Three arms about as
broad as the three egg-shaped gates between them. (Differs from _Hexapyle
triangula_ only by the delicate network of both triangular convex covering
plates, which close the open gates.) Six larger and many smaller spines on
the margin of the disk.
_Dimensions._--Diameter of the disk 0.15, of the gates 0.05.
_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.
2. _Pylodiscus sexangularis_, n. sp.
Cortical shell hexangular, equilateral, four times as broad as the
circular, _Triopyle_-shaped medullary shell. Surface spiny. Three arms
nearly of the same form and size as the three triangular gates between
them. (Similar to _Hexapyle sexangularis_, but differing in the irregular
loose network closing the gates.)
_Dimensions._--Diameter of the disk 0.18, of the gates 0.06.
_Habitat._--North Pacific, south of Japan, Station 237, surface
{571}3. _Pylodiscus cardiopylus_, n. sp.
Cortical shell hexangular, equilateral, five times as broad as the
triangular, _Triopyle_-shaped medullary shell. Surface smooth. Three arms
triangular, at the distal end as broad as the three heart-shaped gates. On
the margin six strong pyramidal spines in the equatorial plane (adradial,
as prolongations of the lateral arm-edges).
_Dimensions._--Diameter of the disk 0.15, of the gates 0.05.
_Habitat._--Indian Ocean, Sunda Strait, Rabbe.
4. _Pylodiscus nephropylus_, n. sp.
Cortical shell circular, three times as broad as the circular,
_Triopyle_-shaped medullary shell. Surface spiny. Three arms trapezoidal,
half as broad as the three kidney-shaped gates. On the margin twelve
stronger, conical, radial spines, opposite in pairs on both sides of the
disk, disposed in six pairs at the distal end of the arms.
_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.06.
_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.
Subfamily 3. DISCOPYLIDA, Haeckel.
_Definition._--#Pylodiscida# with _Triopyle_-shaped medullary shell and
_Pylodiscus_-shaped cortical shell, which is surrounded by a marginal
chambered equatorial girdle.
Genus 251. _Discozonium_,[290] n. gen.
_Definition._--#Pylodiscida# with _Triopyle_-shaped medullary shell and
_Pylodiscus_-shaped cortical shell, which is surrounded by an equatorial
chambered girdle. No peculiar osculum on the margin of the disk.
The genus _Discozonium_ and the following _Discopyle_ make up together the
small group of the Discopylida, or those Pylodiscida in which a discoidal
shell like _Pylodiscus_ is surrounded by a marginal equatorial girdle; this
girdle is divided into twelve to twenty-four or more chambers by radial
beams, which are the external prolongations of the radial marginal spines
of _Pylodiscus_. The latter genus bears therefore to _Discozonium_ the same
relation as _Sethodiscus_ in the other #Discoidea# does to _Lithocyclia_,
or _Phacodiscus_ to _Coccodiscus_.
1. _Discozonium cyclonium_, n. sp.
Disk circular, lenticular, with smooth margin, three times as broad as the
triangular, _Triopyle_-shaped medullary shell. Three gates of the cortical
shell kidney-shaped, twice as broad as the three {572}arms. Chambered
equatorial girdle with twenty to twenty-four subregular chambers (similar
to _Discopyle osculata_, Pl. 48, fig. 19, but without any marginal
osculum).
_Dimensions._--Diameter of the disk 0.2, of the cortical shell 0.14, of the
medullary shell 0.07.
_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.
2. _Discozonium trigonium_, n. sp.
Disk triangular, with thorny margin, four times as broad as the triangular,
_Triopyle_-shaped medullary shell. Three gates of the cortical shell
egg-shaped, scarcely as broad as the three arms. Chambered equatorial
girdle with twenty-four to thirty irregular chambers.
_Dimensions._--Diameter of the disk 0.24, of the cortical shell 0.2, of the
medullary shell 0.06.
_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.
3. _Discozonium hexagonium_, n. sp. (Pl. 48, fig. 18).
Disk hexagonal, with spiny margin, four times as broad as the triangular,
_Triopyle_-shaped medullary shell. Three gates of the cortical shell
kidney-shaped, one and a half times as broad as the arms. Chambered
equatorial girdle with twelve large regular chambers; the radial beams
between them are prolonged into twelve strong pyramidal marginal spines
(three perradial on the ends of the arms, three interradial on the radii of
the gates, six adradial between the former and latter).
_Dimensions._--Diameter of the disk 0.2, of the cortical shell 0.12, of the
medullary shell 0.05.
_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.
Genus 252. _Discopyle_,[291] n. gen.
_Definition._--#Pylodiscida# with _Triopyle_-shaped medullary shell and
_Pylodiscus_-shaped cortical shell, which is surrounded by an equatorial
chambered girdle. One peculiar osculum, surrounded by a corona of spines,
on the margin of the disk.
The genus _Discopyle_ differs from the preceding genus _Discozonium_ in the
development of a peculiar marginal osculum, and bears therefore to it the
same relation as, in the Porodiscida, _Ommatodiscus_ does to _Porodiscus_
(compare above, p. 500). This peculiar osculum is here also surrounded by a
corona of spines, and serves probably for the exit or outlet of a bunch of
pseudopodia or a "sarcode-flagellum." Only two species of _Discopyle_ have
been observed, which represent perhaps better two different genera; in one
species the disk is circular, in the other elliptical. In this latter the
osculum lies on one pole of the main axis.
{573}1. _Discopyle osculata_, n. sp. (Pl. 48, fig. 19).
Disk circular with spiny margin, three times as broad as the triangular,
_Triopyle_-shaped medullary shell. Three gates of the cortical shell
kidney-shaped, on the inside with an interradial spine, twice as broad as
the three pentagonal arms. Chambered equatorial girdle with twenty-four
subregular chambers, in the radius of one odd gate with a large marginal
osculum, which is as broad as the medullary shell, and surrounded by a
dense corona of twenty to thirty strong conical spines.
_Dimensions._--Diameter of the disk 0.15, of the cortical shell 0.1, of the
medullary shell 0.05, of the marginal osculum 0.06.
_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.
2. _Discopyle elliptica_, n. sp. (Pl. 48, fig. 20).
Disk elliptical, four-fifths as broad as long, with spiny margin, three
times as broad as the triangular, _Triopyle_-shaped medullary shell. Three
gates of the cortical shell roundish, on the inside with an interradial
spine, little broader than the quadrangular arms. Chambered equatorial
girdle with twenty to thirty irregular chambers, on one pole of the main
axis with a large marginal osculum, which is one-third as broad as the
length of the main axis, and armed with a corona of twenty to thirty short
conical spines. The osculum does not correspond to a certain radius.
_Dimensions._--Diameter of the disk 0.15, of the cortical shell 0.08, of
the medullary shell 0.04, of the marginal osculum 0.05.
_Habitat._--Central Pacific, Station 267, depth 2700 fathoms.
Family XXIII. #SPONGODISCIDA#, Haeckel (Pl. 41, fig. 11).
_Spongodiscida et Spongocyclida_, Haeckel, 1862, Monogr. d. Radiol.,
pp. 452, 460, 469.
_Spongodiscida_, Haeckel, 1881, Prodromus, p. 461.
_Calodictya_, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss.
Berlin, p. 53 (_partim_).
_Definition._--#Discoidea# without a phacoid shell, with a flat discoidal
shell, in which a simple spherical central chamber is surrounded by an
irregular spongy framework (sometimes with concentric rings around the
central chamber). Surface of the disk quite spongy, without porous
sieve-plates.
The family #Spongodiscida# is the sixth and last family of the #Discoidea#,
and bears to the other families of this group the same relation as the
family Spongosphærida does to the other #Sphæroidea#, or the Spongurida to
the other #Prunoidea#. Its characteristic structure consists in the
irregular spongy framework of the disk, and mainly in the rough, irregular
shape of its spongy surface, which is never covered with porous plates
(neither phacoid shell nor corresponding sieve-plates), as in all other
#Discoidea#. Of course a little spongy structure occurs also in many
Porodiscida {574}and even in some Coccodiscida (principally in the
peripheral part of the disk or its chambered arms); but both flat (or
convex) surfaces of the disk (at least in the central part) remain here
constantly as simple lattice-plates, whilst in all Spongodiscida the whole
surface of the disk is spongy.
When I constituted the family Spongodiscida in my Monograph (1862, pp. 452,
460) I had separated from them the Spongocyclida, exhibiting in the central
part of the disk a more or less distinct concentric arrangement of the
spongy chambers, whilst in the former the delicate spongy framework is
quite irregular, composed of branched siliceous threads, connected and
interwoven in all directions. But in all Spongocyclida the whole surface of
the spongy disk is quite as irregularly rough and deprived of smooth
sieve-plates as in all true Spongodiscida, and the more or less concentric
structure of the central part of the disk in the former (very variable and
often scarcely able to be recognised) seems not sufficient to separate both
groups; even the single genera cannot be sufficiently separated by this
character. I now therefore give up entirely the group of Spongocyclida (as
already done in my Prodromus, 1881). Nevertheless the concentric annular
structure in the dark central part of some Spongodiscida is very
interesting as transition to the Porodiscida; it indicates already that the
former are derived from the latter. Even the single genera in both
families are corresponding.
In the new system of "Polycystina," which Ehrenberg gave, 1875 (Abhandl. d.
k. Akad. d. Wiss. Berlin, p. 157), are enumerated under the _Calodictya_
four genera "with spongy disk," viz., _Spongodiscus_, _Rhopalodictyum_,
_Dictyocoryne_, _Spongaster_. Indeed these four genera, which I here
retain, are true Spongodiscida, and must be separated from the other
_Calodictya_, the greater part of which are Porodiscida. The number of
species of true Spongodiscida now amounts to sixty-seven, which I dispose
in thirteen genera.
The whole family may be divided into three subfamilies. The first of these
are the Spongophacida (corresponding to the Trematodiscida among the
Porodiscida), in which the circular margin of the spongy disk bears no
radial appendages; either the margin is quite simple, spongy
(_Spongodiscus_), or surrounded by a hyaline, solid, or porous equatorial
girdle (_Spongophacus_). The disk is either more lenticular (biconvex) or
more flat discoidal (a shortened cylinder), rarely a little biconcave
(thicker at the margin than in the centre). The spongy framework of the
solid disk is either quite irregular (_Spongodisculus_), or in the central
part with concentric circular rings (_Spongocyclia_), or in the central
part spirally convoluted (_Spongospira_).
The second subfamily, Spongotrochida, corresponds to the Stylodictyida
(among the #Porodiscida#), and is distinguished by solid radial spines on
the margin of the disk, disposed in the equatorial plane either irregularly
or regularly (after the same order as in the other families of
#Discoidea#).
The third subfamily, Spongobrachida, correspond perfectly to the
Euchitonida {575}(among the Porodiscida), bearing on the disk-margin two,
three, or four spongy arms, commonly disposed regularly in the equatorial
plane. Here also occurs the peculiar formation of a "patagium," or of an
interbrachial spongy framework different from that of the arms, which
connects the arms like a web-membrane in the equatorial plane.
The spongy framework exhibits in all these Spongodiscida no remarkable
differences, being everywhere composed of fine branched solid siliceous
threads, interwoven in all directions, with irregular meshes of very
different size.
The central capsule of all Spongodiscida is filled up with the same spongy
framework which covers also both its sides. It grows according to the
enveloping skeleton, but remains constantly smaller. The form of the
central capsule is circular (lenticular or discoidal) in the Spongophacida
and Spongotrochida, whilst in the Spongobrachida it enters into the radial
spongy arms, developed from the margin of the spongy disk.
_Synopsis of the Genera of the Spongodiscida._
{Spongy disk with simple
I. Subfamily { margin (without peculiar
Spongophacida. { equatorialgirdle), 253. _Spongodiscus_.
Spongy disk {
without radial {Spongy disk with a peculiar
appendages. { (solid or porous) equatorial
{ girdle, 254. _Spongophacus_.
{ {Two opposite
{ { spines, 255. _Spongolonche_.
II. Subfamily {Few (two, {
Spongotrochida. { three, or {Three marginal
Spongy disk with { four) radial { spines, 256. _Spongotripus_.
solid radial { spines {
spines on the { regularly {Four crossed
margin (in the { disposed. { spines, 257. _Spongostaurus_.
equatorial {
plane). { {Spines only
{Numerous (five { on the
{ to ten or { margin
{ more) radial { (equatorial), 258. _Stylotrochus_.
{ spines, {
{ often {Spines on both
{ irregularly { sides of the
{ disposed. { disk, 259. _Spongotrochus_.
{ {Without a
{Two arms, { patagium, 260. _Spongolena_.
{ opposite in {
{ one axis. {With a
{ { patagium, 261. _Spongobrachium_.
III. Subfamily {
Spongobrachida. { {Without
Spongy disk with { { a patagium, 262. _Rhopalodictyum_.
spongy radial {Three arms on {
arms on the { the margin. {With a
margin (in the { { patagium, 263. _Dictyocoryne_.
equatorial {
plane). { {Without
{ { a patagium, 264. _Spongasteriscus_.
{Four arms in {
{ cross form. {With a
{ { patagium, 265. _Spongaster_.
Subfamily 1. SPONGOPHACIDA, Haeckel, 1881, Prodromus, p. 461.
_Definition._--#Spongodiscida# with a simple circular disk, without radial
appendages on the margin (neither solid spines nor chambered arms).
{576}Genus 253. _Spongodiscus_,[292] Ehrenberg, 1854, Monatsber. d. k.
preuss. Akad. d. Wiss. Berlin, p. 237.
_Definition._--#Spongodiscida# with a simple circular disk, without radial
appendages and without an equatorial girdle on the margin.
The genus _Spongodiscus_ represents the most simple and primitive form of
the Spongodiscida, or of those #Discoidea# in which the central disk is
more or less spongy, composed of an irregular fine framework. In my
Monograph (1862, pp. 452, 460, 469) I had separated the true _Spongodiscus_
(first described by Ehrenberg, _loc. cit._) and the _Spongocyclia_; the
former being characterised by the irregular spongy framework of the whole
disk, whilst in the latter this framework includes in the central part some
concentric circular rings (approaching _Porodiscus_). In the same way
afterwards Stöhr (1880, _loc. cit._) separated the genus _Spongospira_ as
spongy disks, which include in the central part some spiral convolutions.
But as these differences are rather inconstant and not sharply discernible,
I think it now better to regard these three forms as subgenera of
_Spongodiscus_. All three have the common simple circular disk, without any
marginal appendages.
Subgenus 1. _Spongodisculus_, Haeckel.
_Definition._--Spongy framework of the disk quite irregular, without
concentric rings or spiral convolutions.
1. _Spongodiscus mediterraneus_, Haeckel.
_Spongodiscus mediterraneus_, Haeckel, 1862, Monogr. d. Radiol., p. 461,
Taf. xii. figs. 14, 15.
Spongy disk plain on both sides, with quite an irregular framework, without
concentric rings and without radial piercing beams. Texture everywhere
uniform; meshes eight to ten times as broad as the bars.
_Dimensions._--Diameter of the disk 0.08 to 0.24, of the meshes 0.005 to
0.008.
_Habitat._--Mediterranean (Messina), Haeckel; also fossil in the Tertiary
rocks of Sicily (Grotte), Stöhr.
2. _Spongodiscus radiatus_, n. sp.
Spongy disk plain on both sides, with quite irregular framework, without
concentric rings, but with numerous piercing radial beams which are not
prolonged into marginal spines. Texture everywhere uniform; meshes once and
a half to twice as broad as the bars.
_Dimensions._--Diameter of the disk 0.12 to 0.15, of the meshes 0.002 to
0.003.
_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.
{577}3. _Spongodiscus resurgens_, Ehrenberg.
_Spongodiscus resurgens_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvB. B.
iv., fig. 16.
_Spongodiscus resurgens_, Stöhr, 1880, Palæontogr., xxvi. p. 117, Taf.
vi. fig. 11.
Spongy disk lenticular, biconvex, in the darker centre much thicker than
towards the thin periphery, with an irregular framework, without concentric
rings, but with numerous piercing radial beams. Texture equal; meshes three
to four times as broad as the bars.
_Dimensions._--Diameter of the disk 0.1 to 0.3, of the meshes 0.003 to
0.006.
_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also
fossil in the Tertiary rocks of Sicily and Barbados.
4. _Spongodiscus favus_, Ehrenberg.
_Spongodiscus favus_, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin, p. 301.
Spongy disk lenticular, biconvex, in the darker centre much thicker than
towards the periphery, with an irregular framework, without concentric
rings. Texture different, in the outer half with numerous radial beams and
loose network, the meshes of which are three to four times as large as in
the darker and denser framework of the centre.
_Dimensions._--Diameter of the disk 0.2, of the outer meshes 0.008 to
0.012, of the inner meshes 0.002 to 0.003.
_Habitat._--North Atlantic, Greenland, Færöe Channel (John Murray),
surface.
5. _Spongodiscus biconcavus_, n. sp.
Spongy disk biconcave, in the peripheral, ring-like, thickened part twice
as thick as in the hollowed central part, with an irregular framework,
without concentric rings. Texture different, in the outer half looser than
in the inner, darker part; meshes of the outer part five to six times, of
the inner twice to three times, as broad as the bars.
_Dimensions._--Diameter of the disk 0.25, of the outer meshes 0.01 to
0.012, of the inner 0.004 to 0.006.
_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.
Subgenus 2. _Spongocyclia_, Haeckel, 1862, Monogr. d. Radiol., p. 469.
_Definition._--Spongy framework of the disk in the inner part with
concentric, circular rings, in the outer part irregular.
{578}6. _Spongodiscus cycloides_, Haeckel.
_Spongodiscus cycloides_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 843.
_Spongocyclia cycloides_, Haeckel, 1862, Monogr. d. Radiol., p. 469, Taf.
xxviii. fig. 1.
Spongy disk on both sides plain, in the central part with five to ten
concentric, circular rings, in the peripheral part quite irregularly and
densely spongy. Meshes twice to four times as broad as the bars.
_Dimensions._--Diameter of the disk 0.1 to 0.2, of the meshes 0.003 to
0.006.
_Habitat._--Mediterranean (Messina), North Atlantic (Canary Islands).