Opposed to the Icosacantha, under the na_Report on the Radiolaria Collected by H.M.S. Challenger During the Years 1873-1876, First Part: Porulosa (Spumellaria and Acantharia) Report on the Scientific Results of the Voyage of H.M.S. Challenger During the Years 1873-76, Vol. XVIII

group of Actinelida, in which the number and disposition of the radial

spines is variable, not determined by the Müllerian law. Probably this

group is the common ancestral stock, from which the Icosacantha have been

derived by gradual development of their peculiar disposition. Probably the

oldest and most primitive form of all ACANTHARIA is _Actinelius_, in which

a variable and undetermined (often very large) number of radial spines is

united in one common central point, and therefore forms a needle-sphere.

Whilst here all spines (often more than a hundred) are of equal size and

form, in the nearly allied _Astrolophus_ large and small spines are

intermingled. Both genera together form the small ancestral family of

Astrolophida. In the strange family of Litholophida the radial spines do

not {721}radiate within a spherical space (equally disposed in all

directions), but within a quadrant or even an octant, forming a conical

brush or pencil.

One very remarkable form of #Actinelida# is _Actinastrum_, forming the

transition from these Adelacantha to the common regular Icosacantha. In the

two observed species of _Actinastrum_ we find thirty-two radial spines,

twenty of which are disposed after the Müllerian law, as in the

Icosacantha. The other twelve are four interradial equatorial spines (lying

in the two secondary meridian planes) and eight perradial tropical spines

(lying in the two primary meridian planes). Therefore here in each primary

meridian plane are placed ten spines (two equatorial, four tropical, and

four polar spines), whereas in each secondary meridian plane are placed six

spines (two equatorial and four tropical). But here also all thirty-two

spines are so regularly placed that their free distal ends fall into five

parallel zones, four in each polar zone, eight in each tropical zone, and

eight in the equatorial zone.

_The Central Junction_ of the radial spines in the ACANTHARIA becomes

effected in four different ways:--(1) by simple apposition of the pyramidal

central ends or bases; (2) by a basal leaf-cross, or by broad wings, four

on each spine, supported one upon the other; (3) by a central concrescence

of the meeting bases of all the twenty spines, growing perfectly together;

and (4) by a concrescence in pairs of every two opposite spines. The most

common and probably the original mode of junction is the first--by

pyramidal apposition; the spines at the central base are pointed in the

form of a pyramid, and the triangular faces of the neighbouring pyramids

are simply placed upon one another. Often the small basal pyramids are

imperfectly separated from the spines by an annular constriction. Commonly

the basal pyramids of the four equatorial spines are six-sided, those of

the sixteen other spines five-sided.

The second mode of junction, by a basal leaf-cross, is developed from the

first and appears as a strengthening or a mechanical elaboration of it.

Immediately above the basal pyramid arise from its radial edges four thin

and broad triangular leaves or wings, and the meeting edges of the

neighbouring wings are in apposition one with the other, so that between

the bases of every three or four neighbouring spines a hollow pyramidal

space remains open. The apex of such a pyramidal space is directed towards

the centre of the body, but separated from it by the small basal pyramid;

its open base is directed outwards. The twenty-two hollow pyramidal spaces

are disposed regularly in four different groups:--(A) Four equatorial

spaces, four-sided, each limited by two equatorial and two tropical spines

(one canceral and one capricornal); (B) eight perizonal spaces (four

northern and four southern), four-sided, each limited by one equatorial,

two tropical, and one polar spine; (C) eight peripolar spaces (four

northern and four southern), three-sided, each limited by one tropical and

two polar spines; (D) two polar spaces (one northern and one southern),

four-sided, each limited by four neighbouring polar spines.

{722}The third mode of junction, by central concrescence of all twenty

spines, was formerly regarded by me as an important peculiarity, sufficient

for the separation of subfamilies and genera (Monogr. d. Radiol., 1862, pp.

399, 401; Prodromus, 1881, p. 466). But I found afterwards that in many

species where the twenty spines commonly remain separated, accidentally

they grow perfectly together and form one single piece of acanthin--a

starrulet with twenty rays. Therefore I now think it is more natural to

divide those species only into different subgenera.

A fourth and a very different mode of junction, quite sufficient for the

distinction of different families, is the concrescence in pairs of every

two opposite spines, lying in one diameter (in _Acanthochiasma_ and

_Chiastolus_). Here we obtain a number of "diametral spines" (each composed

of two originally opposed radial spines) and all these diametral spines are

crossed loosely near the central point of the body without any solid and

permanent apposition (Chiastolida). However, in some species of this

peculiar family the central part of the diametral spines is twisted like a

screw or spirally convoluted (Pl. 129, figs. 2, 3).

_The Form of the Radial Spines_ in the ACANTHARIA is extremely varied, and

constitutes the main characters for the distinction of nearly four hundred

species. But all these different forms may be reduced phylogenetically to

three different fundamental forms:--(_a_) the cylindrical (with circular

transverse section), (_b_) the two-edged (with elliptical or lanceolate

transverse section), and (_c_) the four-edged (with square transverse

section). No doubt the first (_a_) is the original primitive form, from

which the two others are secondarily derived. Triangular spines never occur

in the ACANTHARIA, whilst, however, they are common in the #Sphærellaria#.

The first and original form, the cylindrical spine, is either a true

cylinder of equal thickness in its whole length, or it is more or less

conical. Rarely the spine is in the distal half spindle-shaped, and thicker

than in the basal half. The second form, the two-edged spine, is more or

less compressed from two opposite sides; its two edges are either more

blunt, rounded, or more acute, sharp; its transverse section in the former

case is elliptical, in the latter case lanceolate or rhomboidal. Sometimes

the two edges are broader and in the form of two thin opposite wings. The

two-edged spines may be occasionally shorter, triangular or lanceolate, at

other times longer sword-shaped or linear. The third form, the four-edged

spine, has constantly a square transverse section; the sides of this square

are either even or concave; in the latter case the four edges are broadened

and wing-like, but in the former case not. The quadrangular spines are

either prismatic (of equal breadth throughout their whole length) or

pyramidal (becoming gradually thinner towards the distal apex).

_The Apex of the Radial Spines_, or their free distal end, is in the

majority of ACANTHARIA simple, conical. In the minority it is either

truncated or bifid, or four-sided pyramidal, often with two, rarely with

four prominent parallel teeth. In some forms {723}the bifid spines are so

deeply cleft that they become forked. Much more interesting and more varied

than these different forms of the distal end are those of the apophyses of

the radial spines.

_The Apophyses of the Radial Spines_, or their "lateral transverse

processes," are of the greatest importance for the morphological

development of the whole subclass. Only in sixteen among the sixty-five

genera of ACANTHARIA are the apophyses perfectly wanting; in the other

genera they determine in the first place their general character. In the

#Acanthometra# the apophyses remain perfectly free, whilst in the

#Acanthophracta# their meeting ends or branches compose the latticed shell.

All differences in form and shape of the apophyses can be reduced to only

two primary modes; either the spine bears two opposite or four crossed

apophyses; correspondingly all Acantharia apophysaria may be divided into

two different main groups, the Zygapophysica (with two opposite lateral

processes) and the Staurapophysica (with four crossed lateral processes

opposite in pairs). Both groups have probably no direct phylogenetic

connection, but seem to be derived independently from different stocks, and

produce different families. The Zygapophysica are probably derived from

Astrolonchida with two-edged spines (_Zygacantha_), and from this group

arise the Diporaspida, the ancestral group of the majority of

#Acanthophracta#. On the other hand the Staurapophysica are probably

derived from Astrolonchida with four-edged spines (_Acanthonia_), and from

this group arise the Tessaraspida. The apophyses of the #Acanthonida# are

partly simple, partly branched or even latticed; the apophyses of the

#Acanthophracta# are never simple, constantly branched and commonly

latticed.

_The Malacoma_ (or the whole soft body of the ACANTHARIA as opposed to the

skeleton) exhibits some peculiarities which distinguish them from the other

Radiolaria, as well in the structure of the central capsule and its nucleus

as in that of the enveloping extracapsular body and the pseudopodia.

The _Central Capsule_ is constantly spherical in the far greater number of

the ACANTHARIA, viz., in the following six families:--Astrolophida,

Chiastolida, Astrolonchida, Dorataspida, Sphærocapsida, and Phractopeltida.

Among these six families the Astrolonchida and Dorataspida are far greater

and far richer in different forms than all the other families. The central

capsule becomes ellipsoidal or cylindrical, prolonged in one axis, in the

three families, Amphilonchida, Belonapsida, and Diploconida; it becomes

discoidal or lenticular, by the shortening of one axis, in two families,

viz., in the Quadrilonchida and Hexalaspida. Finally, the peculiar family

Litholophida is distinguished by the conical form of its central capsule.

_The Membrane_ of the central capsule in all ACANTHARIA is simple, commonly

thin, sometimes very delicate; in some species it seems to be developed

late, just immediately before the formation of the spores; but in no

species is it completely missing. The membrane is constantly pierced by

innumerable fine pores, for the emission of the {724}pseudopodia; but in

many species (and probably more or less in all ACANTHARIA) there is

recognisable a certain regularity in the disposition of the numerous

pseudopodia and of the pores by which they radiate from the capsule.

Sometimes these pores are disposed in a regular network of ramified lines,

whilst the meshes of this network are devoid of pores; in other cases they

form regular tufts or bushes between the radial spines. Probably in no

ACANTHARIA are the pores of the capsule membrane so numerous and so equally

distributed throughout as in the SPUMELLARIA; we may therefore call the

former ACTIPYLEA (in opposition to the latter, as PERIPYLEA).

_The Nucleus_ of the ACANTHARIA is constantly excentric, whilst it is

originally constantly central in the SPUMELLARIA. This excentric position

is a necessary consequence of the centrogenous development of the radial

spines. Probably connected with this peculiarity is the other, that the

nucleus assumes a peculiar, complicated structure, and that in the greater

number of ACANTHARIA it becomes cleft very early, and that this cleavage is

effected by a peculiar kind of gemmation, first detected and very

accurately described by R. Hertwig (compare his Organismus d. Radiol.,

1879, pp. 10-24). However, in the young ACANTHARIA the nucleus is

constantly simple, and in a certain number of species its cleavage takes

place late (as in the greater number of SPUMELLARIA).

_The Endoplasm_, or the intracapsular sarcode, exhibits in the greater

number of ACANTHARIA a more or less distinct radial arrangement; but this

is often concealed by the different enclosed products of the

endoplasm--oil-globules, vacuoles, red or different coloured

pigment-granules, crystals, &c. Often it encloses a variable number of

"yellow cells" (becoming green by mineral acids) to be considered as

symbiotic xanthellæ.

_The Calymma_ or the jelly-veil, including the central capsule, in the

ACANTHARIA is more or less voluminous, and commonly envelops the skeleton

perfectly. In its surface is sometimes developed a peculiar network of

"supporting fibres." A very peculiar product are the remarkable

"Myophrisca" of the #Acanthometra#, which are wanting in the

#Acanthophracta#; they were first detected by Johannes Müller, and figured

as "Cilien-Kränze," afterwards explained by Hertwig as "contractile Fäden,"

similar to muscular fibrillæ (compare below).

_The Matrix_, placed between the calymma and central capsule, in the

majority of the ACANTHARIA is a rather thin layer of granular exoplasm.

_The Pseudopodia_ arising from it are not so numerous as in the

SPUMELLARIA, and not so equally disposed over the whole surface. Also their

tendency to ramify, anastomose, and form networks seems to be much less

developed. Commonly they are simple or little ramified. In many cases (and

perhaps everywhere) there may be distinguished two different kinds of

pseudopodia:--(1) Axopodia, or permanent pseudopodia (with axial

filaments?), piercing the wall of the central capsule, and arising from the

central mass of endoplasm; and (2) Collopodia, or variable pseudopodia

(without axial filaments), arising outside the capsule from the matrix of

extracapsular sarcode or from the {725}exoplasm on the surface of the

calymma. These and other differentiations seem to indicate that the

pseudopodia in the ACANTHARIA are more highly developed than in the

SPUMELLARIA, and justify the denomination of the former as "Actipylea."

_Synopsis of the Orders and Suborders of_ ACANTHARIA.

-------------------------------------------------------------------------

I. ACANTHOMETRA.

Skeleton composed only of acanthinic radial spines not forming a

complete lattice-shell.

-------------------------------------------------------------------------

Radial spines in variable and indefinite number,

disposed irregularly, 1. #Actinelida#.

Radial spines constantly twenty, disposed regularly

after the Müllerian law of Icosacantha, 2. #Acanthonida#.

-------------------------------------------------------------------------

II. ACANTHOPHRACTA.

Skeleton composed of twenty acanthinic radial spines (disposed after

the Müllerian law) and of a spherical or variously shaped complete

lattice-shell.

-------------------------------------------------------------------------

Radial spines all twenty of equal size; shell and

central capsule spherical, 3. #Sphærophracta#.

Radial spines of different sizes; shell and central

capsule ellipsoidal, discoidal, or heteromorphous, 4. #Prunophracta#.

----

Order III. ACANTHOMETRA, Johannes Müller, 1855.

_Acanthometra_, J. Müller, 1855, Monatsber. d. k. preuss. Akad. d. Wiss.

Berlin.

_Acanthometrida_, Haeckel, 1862, Monogr. d. Radiol., p. 371.

_Acanthometrea_, R. Hertwig, 1879, Organismus d. Radiol., p. 133.

_Acanthonida et Litholophida_, Haeckel, 1881, Prodromus, pp. 465, 469.

_Definition._--ACANTHARIA without complete latticed shell.

The order #Acanthometra#, the third order of Radiolaria, comprises all

those ACANTHARIA in which the acanthinic skeleton is only composed of

radial spines arising from one common central point, but never forms a

complete latticed shell. By the absence of such a latticed or fenestrated

shell the #Acanthometra# differ principally from the nearly allied

#Acanthophracta#, the second order of ACANTHARIA, which constantly possess

such a complete shell.

Johannes Müller, who first detected and described the #Acanthometra# (in

1855, _loc. cit._), defined them as follows:--"Radiolaria without shell,

with siliceous radial spines" (1858, Abhandl. d. k. Akad. d. Wiss. Berlin,

p. 46). He described and figured eighteen species of them, disposed in four

genera (_Acanthometra_ with fifteen species, and _Zygacantha_,

_Lithophyllium_, _Lithoptera_, each with a single species). Among those

eighteen species, however, were two "Acanthometræ cataphractæ,"

appertaining to the following order, the #Acanthophracta#.

In my Monograph (1862, p. 371) all true #Acanthometra# were united into a

single family, Acanthometrida, with the following definition:--"Skeleton

composed of a number of radial spines, piercing the central capsule and

united in its centre, without {726}latticed shell." In the majority of them

I observed that the skeleton did not consist of silex, but of a very

peculiar organic substance, which I called "acanthin." At that time I

divided the family Acanthometrida into four subfamilies:--(1)

Acanthostaurida, (2) Astrolithida, (3) Litholophida, (4) Acanthochiasmida.

The two former now represent the suborder #Acanthonida#, the two latter the

suborder #Actinelida#. The number of genera which I distinguished in my

Monograph amounted to nine, the number of species to fifty. By the rich

collections of the Challenger this number is so much increased that we can

here describe twenty-seven genera and one hundred and sixty species.

Richard Hertwig in his work on the Organismus der Radiolarien (1879, pp.

6-25) adopted my family Acanthometrida, and gave a very accurate

description of its anatomical structure. He confirmed my observations that

the radial spines of this family are never hollow, but solid, and that

their chemical substance is not silex, but the organic matter "acanthin."

He found that the simple nucleus of the Acanthometrida is commonly very

early cleft, and that the peculiar brushes of filaments on the calymma,

described by Johannes Müller and by me as "Gallert-cilien," are peculiar

"contractile filaments," comparable to the "muscle-fibrillæ" of some

Infusoria, or the "Myophan-filaments" (Myophrisca).

The order #Acanthometra# is here divided into two different suborders of

very unequal extent and value, the #Actinelida# and #Acanthonida#. The

first may be regarded as the common ancestral stock, not only of the

second, but of all ACANTHARIA. In the small group of #Actinelida# the

number of radial spines is variable and commonly indefinite, often very

large (more than a hundred); they are therefore Adelacantha. The second

suborder, the #Acanthonida#, comprise by far the greatest part of the

order, and possess constantly twenty radial spines, regularly disposed

after the Müllerian law; they are therefore (like all #Acanthophracta#)

Icosacantha (compare above, p. 717).

The #Actinelida# possess constantly simple radial spines, without any

apophyses; their form is commonly very simple and primitive. This suborder

comprises three small but very different families, the Astrolophida,

Litholophida, and Chiastolida. The first family, the Astrolophida, is the

original ancestral group. A large and variable, commonly indefinite number

of radial spines is here united in the centre of the spherical central

capsule and radiating within a spherical space. In the second family, the

Litholophida, a small and variable number of radial spines (between ten and

twenty) is united in the apex of a conical central capsule and radiating

within the quadrant or octant of a spherical space. In the third family,

the Chiastolida, a variable number of radial spines is grown together by

pairs, in such a manner that every two opposite spines (placed originally

in one axis of the spherical central capsule) forms a single "diametral

spine"; all these diametral spines are not united in the centre of the

central capsule but only crossed loosely near the centre.

{727}The #Acanthonida#, the second suborder of #Acanthometra#, embraces by

far the greatest number in this order, viz., all those forms in which

twenty radial spines are regularly disposed after the Müllerian

law--Icosacantha (compare above, p. 717). The radial spines of this

suborder are either simple or provided with transverse processes (either

two opposite or four crossed apophyses). They are commonly united in the

middle of the central capsule by their opposed basal ends, forming small

pyramids; the meeting triangular faces of the neighbouring pyramids being

propped one upon another. Above these small basal pyramids often arises a

basal leaf-cross formed by four broad triangular leaves or wings with

straight edges; the meeting thin edges of the neighbouring spines serve for

strengthening the basal junction and form hollow pyramidal spaces or

compartments, filled with the contents of the central capsule (compare p.

721). The suborder #Acanthonida# comprises three different families, the

Astrolonchida, Quadrilonchida, and Amphilonchida. The first family, the

Astrolonchida, comprises by far the greater number of the #Acanthonida#;

those genera in which all twenty spines are perfectly equal or nearly equal

in size and form. In the second family, the Quadrilonchida, the four

equatorial spines are much larger (and often also of another form) than the

sixteen other spines (often also the eight tropical larger than the eight

polar spines). The third family, the Amphilonchida, is distinguished by the

preponderating development of only two opposite equatorial spines, which

are much larger (and often also of another form) than the eighteen other

spines.

_Synopsis of the Suborders and Families of_ #Acanthometra#.

-------------------------------------------------------------------------

Suborder I. ACTINELIDA.

Number of the radial spines variable, either more or less than twenty,

commonly disposed irregularly and not according to the Müllerian law.

-------------------------------------------------------------------------

Radial spines very numerous (thirty to a hundred

or more), radiating from a common centre

within a spherical space, 1. ASTROLOPHIDA.

Radial spines between ten and twenty, radiating

from one common point within a sphere-quadrant, 2. LITHOLOPHIDA.

Radial spines of variable number; every two

opposite spines grown together in the centre;

therefore numerous diametral spines are

crossed freely in the centre, 3. CHIASTOLIDA.

-------------------------------------------------------------------------

Suborder II. ACANTHONIDA.

Number of the radial spines constantly twenty, disposed regularly

according to the Müllerian law.

-------------------------------------------------------------------------

All twenty radial spines nearly equal, and of

the same size and form, 4. ASTROLONCHIDA.

Four equatorial spines much larger than (and

often also of different form from) the sixteen

other spines, 5. QUADRILONCHIDA.

Two opposite equatorial spines (or principal

spines) much larger than (and often also of

different form from) the eighteen other

spines, 6. AMPHILONCHIDA.

{728}----

Suborder I. ACTINELIDA, Haeckel, 1882.

_Definition._--#Acanthometra# with a variable number of radial spines,

which are commonly irregularly disposed, not according to the Icosacantha.

Family XXXIII. #ASTROLOPHIDA#, Haeckel.

_Astrolophida_, Haeckel, 1881, Prodromus, p. 469.

_Definition._--#Acantharia# with a variable number of simple radial spines,

radiating within a spherical space from one common central point which is

the centre of the spherical central capsule. No lattice shell.

The family #Astrolophida# comprises the simplest and the most primitive

forms among all ACANTHARIA, and may therefore be regarded as the common

ancestral stock of this whole legion or subclass of Radiolaria. The

acanthinic skeleton is composed of a variable number of quite simple radial

spines, which are united in the centre of the spherical central capsule and

radiate, piercing its walls and the surrounding jelly-veil, within a

spherical space.

The first observed form of this family is the ancestral genus _Actinelius_,

two different species of which I detected in 1864 in the northern

Mediterranean, at Villafranca, near Nice (compare Zeitschr. f. wiss. Zool.,

1865, Bd. xv. p. 364, Taf. xxvi. fig. 4). Three other species of the same

genus were afterwards found by me in the Challenger collections. Whilst in

this _Actinelius_ all radial spines are of the same size, a new nearly

allied genus, _Astrolophus_ (with two species), differs from it by the

different size of the radial spines, a small number of very large spines

being intermingled with a very large number of small spines. In these two

genera, _Actinelius_ and _Astrolophus_ (the true "Astrolophida" _sensu

strictiori_), the number of the radial spines is quite indeterminable and

their arrangement quite irregular and variable.

A third remarkable genus, _Actinastrum_, differs from these two genera in

the definite number and regular order of thirty-two radial spines, and may

therefore perhaps better represent a peculiar family, Actinastrida. In this

genus (of which two species were observed) the thirty-two radial spines are

disposed in such a regular manner that they lie in four meridian planes,

and that their distal ends fall into five parallel zones. These five zones

and these four planes are the same as we find in all Icosacantha (compare

above, p. 717). Also the constant twenty spines of these latter are present

in _Actinastrum_; but their number is here enlarged by twelve other spines

missing in the Icosacantha; four of these are secondary or interradial

equatorial spines, lying opposite in pairs between the four primary or

perradial equatorial spines; and eight are perradial tropical spines, lying

between the eight interradial tropical spines. Therefore the {729}distal

ends of the thirty-two radial spines are disposed regularly in five

parallel zones, and while two zones (the two polar) contain only the points

of every four spines, three zones (the single equatorial and the two

tropical) contain the points of every eight spines. The four meridian

planes are in _Actinastrum_ the same as in the Icosacantha, crossed in the

spineless axis at angles of 45°. But in the Icosacantha each of the two

perradial meridian planes contains six radial spines (two equatorial and

four polar), each of the two interradial meridian planes only four tropical

spines. Whereas in _Actinastrum_ each of the two primary or perradial

meridian planes contains ten spines (two equatorial, four tropical, and

four polar), each of the two secondary or interradial meridian planes six

spines (two equatorial and four tropical). We find therefore altogether

thirty-two radial spines in three orders; eight equatorial, sixteen

tropical, and eight polar spines.

Only one other genus of Radiolaria exhibits the same characteristic

disposition of thirty-two radial spines as _Actinastrum_, and this is

_Chiastolus_; but here the two opposite spines of each pair are grown

together and form one diametral spine; and the sixteen diametral spines are

crossed in the centre of the capsule. In _Actinastrum_, as in _Astrolophus_

and _Actinelius_, the central ends or bases of all the spines are

pyramidal, and the triangular faces of the neighbouring spines rest one

upon another (as in the greater number of #Acanthonida#). The form of the

radial spines in all Astrolophida is quite simple, without lateral

processes or apophyses; chiefly cylindrical, more rarely compressed,

two-edged or quadrangular.

The central capsule in all Astrolophida is spherical, and in the younger

specimens contains a single large concentric and lobed nucleus, but in the

older specimens a large number of small nuclei. The surrounding jelly-veil

or calymma seems commonly to envelop the spines perfectly. The piercing

pseudopodia radiate everywhere between the spines, and are very numerous

and thin. The circulating granules in them are sometimes red (_Actinelius

purpureus_).

_Synopsis of the Genera of Astrolophida._

Radial spines of indefinite {Spines of equal size, 317. _Actinelius_.

number and of irregular {

disposition. {Spines of unequal size, 318. _Astrolophus_.

Radial spines thirty-two, disposed regularly

in five parallel zones, 319. _Actinastrum_.

Genus 317. _Actinelius_,[357] Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd.

xv. p. 364.

_Definition._--#Astrolophida# with a variable and undetermined number of

simple radial spines, all of equal size, united in the centre of the

spherical central capsule.

{730}The genus _Actinelius_ comprises the most simple and primitive forms

among all ACANTHARIA, and may be regarded as the common ancestral stock of

this whole legion. The spherical central capsule is pierced by numerous

simple radial spines of equal size, the pyramidal bases of which are

supported one upon another with their triangular faces in the centre of the

capsule. The number and position of the spines are quite indefinite and

variable. We may derive _Actinelius_ either from _Actissa_ (#Colloidea#) by

development of acanthinic radial spines, or directly from _Actinosphærium_

(Heliozoa) by formation of a central capsule.

Subgenus 1. _Actinelarium_, Haeckel.

_Definition._--Radial spines cylindrical, conical, or spindle-shaped, their

transverse section circular.

1. _Actinelius primordialis_, n. sp. (Pl. 129, fig. 1).

Spines sixty to eighty or more, cylindrical, at the distal end thickened,

spindle-shaped. Apex simple. Base a small slender pyramid. Central capsule

yellow. Granules of the sarcode colourless.

_Dimensions._--Length of the spines 0.3 to 0.4, breadth in the distal part

0.02, in the basal part 0.008.

_Habitat._--Central Pacific, Stations 265 to 274, surface.

2. _Actinelius purpureus_, Haeckel.

_Actinelius purpureus_, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv.

p. 364, Taf. xxvi. fig. 4.

Spines thirty to forty or more, cylindrical, very thin, a little thinner

towards both ends. Apex simple. Base a small sulcate pyramid. Central

capsule opaque, purple. Granules of the sarcode also purple.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth 0.002.

_Habitat._--Mediterranean (Nice), Haeckel.

Subgenus 2. _Actinelidium_, Haeckel.

_Definition._--Radial spines compressed, two-edged; their transverse

section elliptical or lanceolate.

3. _Actinelius protogenes_, n. sp.

Spines fifty to sixty, compressed, two-edged, gradually broadened towards

the truncated distal end. Basal or proximal end thin, pyramidal. The spines

of this species are similar to those of {731}_Actinastrum pentazonium_ (p.

733) and of _Chiastolus amphicopium_ (Pl. 129, fig. 3), but much more

numerous, smaller, and not regularly disposed. These latter two Actinelida

must be separated on account of the regular disposition of the thirty-two

spines.

_Dimensions._--Length of the spines 0.2, basal breadth 0.008, distal

breadth 0.02.

_Habitat._--South Pacific, Station 165, surface.

Subgenus 3. _Actinelonium_, Haeckel.

_Definition._--Radial spines quadrangular, prismatic, or pyramidal, their

transverse section square.

4. _Actinelius pallidus_, Haeckel.

_Actinelius pallidus_, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv.

p. 364.

Spines eighty to one hundred and twenty or more, quadrangular, prismatic,

of equal breadth throughout their whole length. Apex simple, truncate or

pyramidal. Base a four-sided slender pyramid. Central capsule pale

yellowish. Granules of the sarcode colourless.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth 0.005.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific.

5. _Actinelius polyacanthus_, n. sp.

Spines two hundred to three hundred or more, quadrangular, pyramidal,

gradually thinned towards the simple apex. Base a small three-sided

pyramid. Central capsule opaque.

_Dimensions._--Length of the spines 0.12 to 0.18, basal breadth 0.012.

_Habitat._--South Pacific, Station 291, surface.

Genus 318. _Astrolophus_,[358] Haeckel, 1881, Prodromus, p. 469.

_Definition._--#Astrolophida# with a variable and undetermined number of

simple radial spines of different sizes (large and small spines

intermingled), which are united in the centre of the spherical central

capsule.

The genus _Astrolophus_ differs from the nearly allied ancestral genus

_Actinelius_ only in the unequal size of the numerous radial spines. In

both observed species very numerous small spines are intermingled with a

small number of large spines, and between them numerous spines of medium

size. The small spines fill up the hollow spaces between the basal parts of

the large spines.

{732}1. _Astrolophus stellaris_, n. sp.

Radial spines from one hundred to two hundred, of very different sizes, but

of similar form; about sixteen to twenty very large spines, forty to fifty

of medium size, and one hundred to one hundred and twenty much smaller. All

spines cylindrical in the greater part of their length, with simple apex,

gradually thickened towards the central part, conical, without edges. The

base itself is a slender pyramid with four to eight edges.

_Dimensions._--Length of the largest spines 0.3 to 0.4, of the majority 0.1

to 0.2, of the smallest 0.05 to 0.1.

_Habitat._--South Pacific, Station 288, surface.

2. _Astrolophus solaris_, n. sp. (Pl. 132, figs. 12_a_, 12_b_).

Radial spines from two hundred to three hundred, of very different sizes,

but of similar form; about twenty to thirty very large spines, sixty to

eighty of medium size, and one hundred and twenty to one hundred and fifty

much smaller. All spines cylindrical in the greater part of their length,

with simple apex, gradually thickened and four-edged towards the central

base. The base itself is a slender pyramid with four to eight edges; partly

the faces, partly the edges of these basal pyramids rest one upon another,

the points of the larger spines meeting in the centre.

_Dimensions._--Length of the largest spines 0.4 to 0.5, of the majority 0.2

to 0.3, of the smallest 0.1 to 0.16; basal thickness of the largest spines

0.015.

_Habitat._--South-east Pacific (off Juan Fernandez), Station 296, surface.

Genus 319. _Actinastrum_,[359] n. gen.

_Definition._--#Astrolophida# with thirty-two simple radial spines,

regularly disposed within four meridian planes in such an order that their

distal ends fall into five parallel zones. Central ends of the thirty-two

spines supported one upon another in the centre of the spherical central

capsule.

The genus _Actinastrum_ differs from the two preceding genera in the

definite number and order of the thirty-two radial spines, which are

disposed in a very remarkable manner. Twenty radial spines are disposed

after the Müllerian law of Icosacantha (compare above, p. 717). The

remaining twelve spines are four equatorial spines lying in the two

secondary meridian planes, and eight tropical spines lying in the two

primary meridian planes. We have therefore together eight equatorial,

sixteen tropical, and eight polar spines (compare above, p. 729).

{733}1. _Actinastrum legitimum_, n. sp.

All thirty-two radial spines of equal size and similar form, cylindrical,

conical at the distal end, at the central base pyramidal. Central capsule

pellucid, colourless.

_Dimensions._--Length of the radial spines 0.3, breadth 0.004.

_Habitat._--South Pacific, Station 288, surface.

2. _Actinastrum pentazonium_, n. sp.

All thirty-two radial spines of equal size and similar form, compressed,

two-edged, gradually becoming broader and thinner from the pyramidal

central base towards the truncated distal end. Central capsule dark,

opaque. (Compare the similar _Chiastolus amphicopium_, Pl. 129, fig. 3.)

_Dimensions._--Length of the radial spines 0.2, breadth at the base 0.005,

at the distal end 0.02.

_Habitat._--South Pacific (west coast of Patagonia), Station 302, surface.

Family XXXIV. LITHOLOPHIDA, Haeckel.

_Litholophida_, Haeckel, 1862, Monogr. d. Radiol., p. 401.

_Definition._--ACANTHARIA with a variable number of simple radial spines

radiating within a conical space (or within the quadrant of a sphere) from

one common central point, which is the apex of the conical central capsule.

No lattice-shell.

The family #Litholophida#, represented only by a single genus,

_Litholophus_, differs from all other ACANTHARIA in the remarkable fact

that the common point, from which the radial spines arise, is not the

geometrical central point of the whole body, but is quite excentric in

position, the apex of the conical or pyramidal central capsule. Therefore

the spines form together a kind of brush or broom.

When I founded the family Litholophida in my Monograph (1862, p. 401) I

knew only a single species, _Litholophus rhipidium_, observed very

frequently in Messina. Another species, _Litholophus ligurinus_, was

afterwards (1864) found by me at Nice. Six other species were detected in

the preparations of the Challenger, some of them very frequent. All these

eight species of _Litholophus_ are very nearly allied, and exhibit only

slight differences in the form and number of the radial spines; their mode

of excentric connection and the structure of the peculiar soft body is

everywhere the same.

The radial spines in all observed Litholophida possess the form of the

genus _Acanthonia_, _i.e._, they are quite simple, four-sided prismatic or

quadrangular, with square transverse section; their four edges are

sometimes smooth, at other times elegantly denticulate, commonly more or

less prominent or wing-shaped. In the greater number of species they are

very long and of nearly equal breadth, prismatic; in some species they are

more pyramidal, thinned towards the distal end; the latter {734}is commonly

truncated or broken off, sometimes pyramidal. The central end is everywhere

thinned, more or less pyramidal, and the neighbouring spines are propped

one upon another by the triangular faces of their small basal pyramids. A

slight pressure is sufficient to destroy their connection.

The number and disposition of the radial spines seem to be variable and

irregular, but require further researches. In four of the observed eight

species I found constantly ten spines, in two other species from ten to

twenty (commonly twelve or sixteen), and in two species twenty or more. A

certain order or disposition of the spines within the conical space in

which they radiate could nowhere be ascertained.

When I first observed _Litholophus_, I supposed that it might only be a

mutilated or altered form of an _Acanthonia_. Afterwards, observing many

specimens with ten spines, I was led to the suggestion that they were

produced by self-division of an _Acanthonia_, and that the number of the

spines in each half of the body might be afterwards doubled. But this

suggestion seems to be refuted by the fact that in no other genus of the

numerous ACANTHARIA is self-division observed, and that many hundreds of

_Litholophus_ which I observed exhibit quite constantly only a single form

of radial spines, that of _Acanthonia_--simple quadrangular spines without

any apophyses.

Genus 320. _Litholophus_,[360] Haeckel, 1862, Monogr. d. Radiol., p. 401.

_Definition._--#Litholophida# with a variable number of quadrangular

diverging radial spines, united with pyramidal bases in the apex of the

conical central capsule.

The genus _Litholophus_, the only one of this family, exhibits the

peculiarities just described, but might more nearly be defined as a typical

"genus" by the quadrangular form of the radial spines, identical with those

of _Acanthonia_.

The central capsule of _Litholophus_ is constantly conical or pyramidal,

commonly opaque, of a dark brownish or reddish colour; it contains many

small nuclei. It envelops the basal half of all radial spines in such a

manner that their basal parts are united in its apex, and their distal

parts pierce the rounded base of the conical capsule (Pl. 129, fig. 2).

The calymma or the jelly envelope of the central capsule is only developed

at its base, where the spines radiate; at the conical mantle of the capsule

it is very thin. The spines seem to be perfectly enclosed in the calymma

and connected with it by the same contractile retinacula or "myophrisca"

which we observe in the #Acanthonida#. The pseudopodia arise only from the

rounded base of the conical capsule, and radiate between the spines,

piercing the calymma, diverging within the conical space occupied by the

fascicle of spines.

{735}Subgenus 1. _Litholopharium_, Haeckel.

_Definition._--Ten radial spines.

1. _Litholophus decimalis_, n. sp.

Ten radial spines, four-sided prismatic, with prominent smooth edges, of

equal breadth throughout their whole length.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth 0.006.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific,

surface.

2. _Litholophus pyramidalis_, n. sp.

Ten radial spines, four-sided pyramidal, with prominent smooth edges,

gradually thickened from the small pyramidal base towards the truncated

distal end.

_Dimensions._--Length of the spines 0.3 to 0.4, breadth in the basal part

0.002, in the middle part 0.006, in the distal part 0.012 to 0.02.

_Habitat._--Central Pacific, Station 266, surface.

3. _Litholophus decapristis_, n. sp. (Pl. 129, fig. 2).

Ten radial spines, four-sided prismatic, with prominent, elegantly

denticulated edges, of equal breadth in their whole length.

_Dimensions._--Length of the spines 0.2 to 0.4, breadth 0.008.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

4. _Litholophus decastylus_, n. sp.

Ten radial spines, four-winged pyramidal, with broad and thin, elegantly

denticulated edges, gradually thickened from the small pyramidal base

towards the truncated distal end.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth in the basal part

0.002, in the middle part 0.005, in the distal part 0.015.

_Habitat._--South Atlantic, Station 332, surface.

Subgenus 2. _Litholophidium_, Haeckel.

_Definition._--Number of the radial spines variable, between ten and

twenty, commonly twelve to sixteen.

{736}5. _Litholophus ligurinus_, Haeckel.

_Litholophus ligurinus_, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv.

p. 366.

Spines of variable number, from eleven to twenty, commonly twelve to

sixteen, four-sided prismatic, with smooth thin edges, of equal breadth in

their whole length or a little thinner towards the proximal end.

_Dimensions._--Length of the spines 0.3, breadth 0.005.

_Habitat._--Mediterranean (Nice); Central Pacific, Station 274, surface.

6. _Litholophus rhipidium_, Haeckel.

_Litholophus rhipidium_, Haeckel, 1862, Monogr. d. Radiol., p. 402, Taf.

xix. fig. 6.

Spines of variable number, from eleven to twenty, commonly twelve to

sixteen, four-sided prismatic, with distantly denticulated edges, of equal

breadth in their whole length or a little thinner towards both ends.

_Dimensions._--Length of the spines 0.3, breadth 0.006.

_Habitat._--Mediterranean (Messina); North Atlantic, Station 352, surface.

Subgenus 3. _Litholophonium_, Haeckel.

_Definition._--Number of the radial spines twenty (or more?).

7. _Litholophus fasciculus_, n. sp.

Spines constantly (?) twenty, four-sided prismatic, with smooth prominent

edges, nearly of equal breadth throughout their whole length.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth 0.008.

_Habitat._--South Pacific, Station 291, surface.

8. _Litholophus penicillus_, n. sp.

Spines constantly twenty (or more?), four-sided prismatic, with distantly

denticulated edges, gradually thickened from the small pyramidal base to

the middle part, of equal breadth in the distal half.

_Dimensions._--Length of the spines 0.3 to 0.4, breadth 0.005 to 0.007.

_Habitat._--North Pacific, Station 252, surface.

Family XXXV. #CHIASTOLIDA#, Haeckel.

_Acanthochiasmida_, Haeckel, 1862, Monogr. d. Radiol., p. 402.

_Definition._--ACANTHARIA with a variable number of simple radial spines,

which are grown together in pairs (two opposite spines of each pair

representing together a single diametral spine). Diametral spines crossed

loosely in the centre of the spherical or irregular roundish central

capsule. No lattice-shell.

{737}The family #Chiastolida# (or Acanthochiasmida) differs from all other

ACANTHARIA in the peculiar mode of the radial spines; these grown together

in pairs in the centre of the body, so that every two spines opposite in

one axis of the body form together one single diametral spine. All

diametral spines are loosely crossed in the middle of the central capsule,

or connected by a peculiar screw-like winding, but not united firmly.

I established the family Acanthochiasmida in my Monograph (1862, p. 402)

upon the single genus _Acanthochiasma_ (with three species), in which only

ten diametral spines are constantly found; I derived these from the twenty

radial spines of the common #Acanthometra#, supposing that every two

opposite spines of the latter (lying in one axis) were grown together in

the centre, whilst the intimate connection of the twenty radial spines in

the common centre was dissolved. This opinion was afterwards confirmed by

Richard Hertwig, who observed _Acanthochiasma_ intact in the living state.

Although two species of this genus are cosmopolitan and very common, the

number of species is very small; I could add to those three older known

forms only a single new species.

Another genus of this family, _Chiastolus_, was observed by me only in a

single specimen but it is extremely interesting. It has sixteen diametral

spines, disposed quite regularly after the same law of the thirty-two

spines of _Actinastrum_ which we described above (compare above, p. 729).

Therefore we cannot doubt that the former is derived from the latter in the

same way, every two opposite radial spines (of one axis) being grown

together to form a single diametral spine. As we place _Acanthometron_

(with twenty spines) and _Actinastrum_ (with thirty-two spines) in two

different families, it would perhaps be more convenient to separate also

_Acanthochiasma_ and _Chiastolus_ as representatives of two different

families--Acanthochiasmida (with ten diametral spines) and Chiastolida

(with sixteen diametral spines).

As we derive _Acanthochiasma_ from _Acanthometron_ by concrescence in pairs

of the twenty radial spines, the Müllerian law of Icosacantha must be

employed also to the ten diametral spines of the former, therefore two of

them are equatorial, four tropical, and four polar spines. In the same way

we may employ the new law of disposition found in the thirty-two radial

spines of _Actinastrum_ equally to the sixteen diametral spines of

_Chiastolus_, which we derive from the former, four of them are equatorial,

eight tropical, and four polar spines (compare above, p. 732).

_The Central Capsule_ of the Chiastolida is spherical, and exhibits in

general the same shape as in the #Acanthonida#, and specially in the

Astrolonchida. Of course every diametral spine pierces the capsule twice,

at two points diametrically opposed. In some species of _Acanthochiasma_

the central capsule is formed very late, so that it seems often to be

absent. A very accurate description of the capsule and its nucleus, as well

as of the calymma and the pseudopodia, is given by Richard Hertwig in his

Organismus der Radiolarien (1879, pp. 10-18). The pseudopodia are very

numerous, and sometimes bear reddish granules.

{738}_Synopsis of the Genera of Chiastolida._

I. Subfamily Chiastolidina. Sixteen diametral

spines, derived by concrescence of thirty-two

radial spines, 321. _Chiastolus_.

II. Subfamily Acanthochiasmida. Ten diametral

spines, derived by concrescence of twenty

radial spines, 322. _Acanthochiasma_.

Genus 321. _Chiastolus_,[361] n. gen.

_Definition._--#Chiastolida# with sixteen diametral spines, derived from

thirty-two radial spines opposite and grown together in pairs.

The genus _Chiastolus_, hitherto known only by a single observed specimen,

comprises the Chiastolida with sixteen diametral spines, which are loosely

crossed in the centre of the body. Four of these spines are equatorial,

four polar, and eight tropical. We derive _Chiastolus_ from _Actinastrum_

by concrescence of every two opposite spines in one axis of the body

(compare above, pp. 729, 732).

1. _Chiastolus amphicopium_, n. sp. (Pl. 129, figs. 3, 3_a_, 3_b_).

Spines in the central part cylindrical, spirally convoluted in a very

peculiar manner, broadened towards both ends, strongly compressed,

two-edged; the broadest parts are the two truncated distal ends, five to

seven times as broad as the thinnest central part, which is placed between

two spindle-shaped intumescences. These cochleary central parts of the

sixteen spines seem to be resting one upon another. Each spine (composed of

two opposite equal radial spines) has nearly the form of a double oar. The

single observed specimen (preserved in glycerine) exhibited a most regular

disposition of the thirty-two spines (grown together in pairs in the

centre). The diameter of the dark non-transparent spherical central capsule

equalled one-fifth to one-fourth of the total length of the double spines.

When the soft parts of the body were destroyed by sulphuric acid, the

sixteen single spines were suddenly dispersed.

_Dimensions._--Length of the sixteen double spines 0.5, distal breadth (of

the truncated ends) 0.05, central breadth 0.01; diameter of the central

capsule 0.12.

_Habitat._--South-east Pacific (near Juan Fernandez), Station 297, surface.

Genus 322. _Acanthochiasma_,[362] Krohn, 1860, Monatsber. d. k. preuss.

Akad. d. Wiss. Berlin, p. 810.

_Definition._--#Chiastolida# with ten diametral spines, derived from twenty

radial spines opposite and grown together in pairs.

{739}The genus _Acanthochiasma_ with a small number of common species,

comprises the Chiastolida with ten diametral spines, which are loosely

crossed in the centre of the body. I could distinguish only four species,

two of which are cosmopolitan and very widely distributed. In all four

species the diametral spines are quite simple, cylindrical; only in one

species distinguished by a spiral winding or torsion in the middle part,

where they are crossed one to another. We derive _Acanthochiasma_ from

_Acanthometron_ by concrescence of every two spines opposite in one axis of

the body.

1. _Acanthochiasma krohnii_, Haeckel.

_Acanthochiasma krohnii_, Haeckel, 1862, Monogr. d. Radiol., p.403, Taf.

xix. fig. 7.

_Acanthochiasma krohnii_, R. Hertwig, 1879, Organismus d. Radiol., Taf.

ii. fig. 6.

Spines needle-shaped, cylindrical, very thin and long, of equal breadth in

their whole length, distinguished by a high degree of elasticity. Central

capsule colourless or yellowish-white, transparent. Granules of the sarcode

colourless.

_Dimensions._--Length of the spines 0.5 to 1.0, breadth 0.001 to 0.002.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, very

common.

2. _Acanthochiasma rubescens_, Krohn.

_Acanthochiasma rubescens_, Haeckel, 1862, Monogr. d. Radiol., p. 403.

Spines cylindrical, of equal breadth in their whole length, not very

elastic, pointed at the two ends. Central capsule intransparent, reddish,

with violin-shaped concretions. Granules of the sarcode red coloured.

_Dimensions._--Length of the spines 0.2 to 0.6, breadth 0.004 to 0.006.

_Habitat._--North Atlantic, Madeira, Krohn; Lanzerote, Haeckel.

3. _Acanthochiasma fusiforme_, Haeckel.

_Acanthochiasma fusiforme_, Haeckel, 1862, Monogr. d. Radiol., p. 404,

Taf. xix. fig. 8.

Spines spindle-shaped, from the thicker central part thinned towards the

two thin conical ends, perfectly straight and smooth, rigid, inelastic.

Central capsule non-transparent, brown.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth in the central part

0.006 to 0.009.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific.

4. _Acanthochiasma spirale_, n. sp.

Spines spindle-shaped, tapering from the thicker central part towards the

two thin conical ends, rigid, inelastic; their central part is spirally

convoluted in a very peculiar cochlea-like manner, as in _Chiastolus

amphicopium_ (Pl. 129, figs. 3_a_, 3_b_). The ten spines are propped one

upon another by the central screw. Central capsule dark, opaque.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth of the central

spiral part 0.01.

_Habitat._--Central Pacific, Station 266, surface.

{740}----

Suborder II. ACANTHONIDA, Haeckel (Pls. 130-132).

_Acanthonida_, Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Acanthometra# with twenty radial spines, disposed according

to the Müllerian or Icosacanthan law in five zones each of four spines.

Family XXXVI. #ASTROLONCHIDA#, Haeckel (Pl. 130).

_Astrolonchida_, Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Acanthometra# with twenty radial spines of nearly equal

size and similar form, disposed according to the law of the Icosacantha. No

lattice-shell.

The family #Astrolonchida#, the first and oldest of the #Acanthonida#, is

no doubt the ancestral stock not only of this suborder but also all

#Acanthophracta#, _i.e._, of all Icosacantha or all ACANTHARIA in which

twenty radial spines are regularly disposed according to the Müllerian law,

forming five zones each of four alternating spines (compare above, p. 717).

The Astrolonchida differ from the #Acanthophracta# in the absence of a

complete lattice-shell, from the other two families of #Acanthonida# (the

Quadrilonchida and Amphilonchida) in the equal size and similar form of all

the spines. Probably this equality is nowhere quite perfect, since in all

Icosacantha the central bases of the twenty spines exhibit originally

certain slight differences of form and junction, effected by the regular

disposition itself. But setting aside this slight difference, only

recognisable by means of a very accurate investigation of the central

junction (and in thinner spines often not at all recognisable), the twenty

spines of the Astrolonchida appear perfectly equal. Therefore the four

equatorial spines are not distinguished from the sixteen other spines, as

is constantly the case in the two following families.

The number of genera (eleven) and of species (seventy-six) in the

Astrolonchida is far larger than in the five other families of

#Acanthometra#, and requires a distinction into three different

subfamilies. (A) In the Zygacanthida the form of the radial spines is quite

simple, without apophyses or transverse processes; (B) in the

Phractacanthida each spine bears two opposite apophyses (rarely two

longitudinal rows of these opposite apophyses); (C) in the Stauracanthida

each spine bears a cross of four apophyses, opposite in pairs (rarely four

longitudinal crossed rows of apophyses, opposite in pairs). The

Phractacanthida and Stauracanthida appear as two divergent branches of the

pedigree, derived independently from the common ancestral stock of

Zygacanthida.

In the Zygacanthida, constantly devoid of apophyses, we can distinguish

only three genera, characterised by the different fundamental form of the

radial spines; these are:--(1) _Acanthometron_, with cylindrical or conical

spines (without edges); (2) _Zygacantha_, with compressed and two-edged

spines; (3) _Acanthonia_, with four-edged, prismatic or pyramidal spines.

The transverse section of the spines is in the first case {741}circular, in

the second elliptical or lanceolate, in the third square. All the different

forms of spines, which we find in the numerous ACANTHARIA, may be reduced

to these three forms, and among these the second and third are derived from

the first.

The development of apophyses or of lateral transverse processes (wanting in

the Zygacanthida) is of the greatest value for the further differentiation

of the ACANTHARIA. For from the Phractacanthida (with two opposite

apophyses on each spine) we must derive the Phrastaspida, the common

ancestral stock of the Diporaspida (and therefore also the Belonaspida,

Hexalaspida, Diploconida, and Phractopeltida). On the other hand the

Stauracanthida (with four crossed apophyses on each spine) have produced

the Stauraspida, or the ancestral group of the Tessaraspida and

Sphærocapsida. From all these #Acanthophracta#, possessing a complete

lattice-shell, the Astrolonchida differ in the absence of such a complete

shell. Also in the few cases in which the apophyses become latticed

(_Doracantha_ among the Phractacanthida, and _Phatnacantha_ among the

Stauracanthida), the lattice-plates of the neighbouring spines never meet

with their edges, as is the case in all #Acanthophracta#. But in a

phylogenetic as well as in an ontogenetic sense the former are the

ancestral stock of the latter.

_The Central Capsule_ in the Astrolonchida is commonly spherical, sometimes

with twenty roundish elevations or conical papillæ, extending radially to

the basal half of the radial spines. The calymma is voluminous, and forms

around the radial spines conical or cylindrical "jelly-sheaths," which are

connected with the spines by coronas of Myophrisca (or of the bodies

formerly called "Gallert-cilien," afterwards recognised as "contractile

Filamente").

_Synopsis of the Genera of Astrolonchida._

-------------------------------------------------------------------------

I. Subfamily Zygacanthida.

Twenty radial spines simple, without apophyses or lateral transverse

processes.

-------------------------------------------------------------------------

Spines cylindrical, with circular transverse

section, 323. _Acanthometron_.

Spines compressed, two-edged or lamellar, with

elliptical or rhomboidal transverse section, 324. _Zygacantha_.

Spines quadrangular (prismatic or pyramidal), with

four edges, with square transverse section, 325. _Acanthonia_.

-------------------------------------------------------------------------

II. Subfamily Phractacanthida.

Twenty radial spines provided each with two opposite apophyses (or

two longitudinal rows of apophyses).

-------------------------------------------------------------------------

{ Apophyses simple, 326. _Lithophyllium_.

{

Two apophyses opposite on { Apophyses branched, 327. _Phractacantha_.

each spine. {

{ Apophyses latticed, 328. _Doracantha_.

Two opposite longitudinal rows of apophyses (four

to eight or more apophyses on each spine,

opposite in pairs), 329. _Astrolonche_.

-------------------------------------------------------------------------

III. Subfamily Stauracanthida.

Twenty radial spines provided each with four crossed apophyses (or

four crossed longitudinal rows of apophyses).

-------------------------------------------------------------------------

{ Apophyses simple, 330. _Xiphacantha_.

Four apophyses (in cross {

form) opposite in pairs { Apophyses branched, 331. _Stauracantha_.

on each spine. {

{ Apophyses latticed, 332. _Phatnacantha_.

Four longitudinal rows of apophyses, opposite in

pairs in cross form on each spine, 333. _Pristacantha_.

{742}Subfamily 1. ZYGACANTHIDA, Haeckel.

_Definition._--#Astrolonchida# with twenty simple radial spines, without

apophyses or lateral transverse processes.

Genus 323. _Acanthometron_,[363] J. Müller, 1855, Monatsber. d. k. preuss.

Akad. d. Wiss. Berlin, p. 229.

_Definition._--#Astrolonchida# with simple cylindrical or needle-shaped

radial spines, without edges and without apophyses; their transverse

section is circular.

The genus _Acanthometron_, with the restricted definition here given, is

the most simple form of all #Acanthonida#, and may be regarded as the

common ancestral form not only of this suborder but also of all

#Acanthophracta#, in general of all Icosacantha, or all ACANTHARIA in which

twenty radial spines are regularly disposed after the Müllerian law (p.

717). In the wider sense, given originally to #Acanthometra# by Johannes

Müller, its discoverer, this genus comprised all ACANTHARIA constituting

here our order "#Acanthometra#" (Radiolaria without lattice-shell, with

radial spines united in the centre). In my Monograph (1862, p. 375) I

restricted this genus to those "Acanthometrida" in which twenty simple

spines of equal size (and without apophyses) are supported one upon another

in the centre, and I separated as _Astrolithium_ those forms in which they

are grown together in the centre. But this difference now appears not so

important, and I restrict here the genus _Acanthometron_ (not

#Acanthometra#) to those most simple forms in which the simple radial

spines are cylindrical or conical, without edges.

Subgenus 1. _Acanthometrella_, Haeckel.

_Definition._--Spines at the central base without leaf-cross, united by the

opposed triangular faces of their pyramidal bases, resting one upon

another.

1. _Acanthometron elasticum_, Haeckel.

_Acanthometra elastica_, Haeckel, 1862, Monogr. d. Radiol., p. 376, Taf.

xv. fig. 1, Taf. xviii. fig. 1.

_Acanthometra elastica_, R. Hertwig, 1879, Organismus d. Radiol., Taf. i.

figs. 2, 2_a_, 2_b_.

Spines cylindrical, very thin and long, needle-shaped, at the central base

four-sided pyramidal, without leaf-cross. Distal apex conical. The spines

are very elastic, of nearly equal thickness in their whole length. Central

capsule quite pellucid, colourless, with a variable number of yellow

pigment-bodies (xanthellæ?).

_Dimensions._--Length of the spines 0.3 to 0.6, breadth 0.001 to 0.002.

_Habitat._--Cosmopolitan, very common in all warmer seas; Mediterranean,

Atlantic, Indian, Pacific, surface.

{743}2. _Acanthometron cylindricum_, n. sp. (Pl. 130, fig. 2).

Spines cylindrical, thick and long, at the central base thickened with a

pear-shaped knob, and with very small central fulcral pyramid, without

leaf-cross. Distal apex rounded or truncated. Central capsule opaque,

filled with red pigment-bodies.

_Dimensions._--Length of the spines 0.4 to 0.8, breadth 0.01 to 0.015.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

3. _Acanthometron fuscum_, J. Müller.

_Acanthometra fusca_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 47, Taf. xi. fig. 4.

_Acanthometra fusca_, Haeckel, 1862, Monogr. d. Radiol, p. 377.

Spines very thin and long, in the proximal half cylindrical, in the distal

half conical, gradually thinned towards the simple conical apex. Central

base a small four-sided pyramid, without leaf-cross. Central capsule

opaque, filled with brown pigment-bodies.

_Dimensions._--Length of the spines 0.2 to 0.4, breadth 0.002 to 0.004.

_Habitat._--Mediterranean (Cette, Portofino, Messina).

4. _Acanthometron bulbosum_, Haeckel.

_Acanthometra bulbosa_, Haeckel, 1862, Monogr. d. Radiol., p. 377, Taf.

xv. fig. 2, Taf. xviii fig. 2.

Spines very thin and long, cylindrical, with simple needle-shaped apex; in

the basal part conical, towards the centre much thickened, with a short

four-sided fulcral pyramid, without leaf-cross. Central capsule opaque,

filled with brown pigment-bodies.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth in the middle and

outer part 0.001, in the basal part 0.008 to 0.012.

_Habitat._--Mediterranean; Atlantic, Station 354, surface.

5. _Acanthometron dolichoscion_, Haeckel (Pl. 129, figs. 6-8).

_Acanthometra dolichoscia_, Haeckel, 1862, Monogr. d. Radiol., p. 377,

Taf. xviii. figs. 3_a_, 3_b_.

Spines very long and thin, cylindrical, in the thickened outer half about

twice as thick as in the thin inner half, at the simple apex compressed,

two-edged. Central base little thickened, with a small four-sided pyramid,

without leaf-cross. Central capsule transparent, whitish or yellowish.

_Dimensions._--Length of the spines 0.6 to 0.8, breadth in the proximal

part 0.004, in the distal part 0.008.

_Habitat._--Mediterranean (Messina, Portofino), surface.

6. _Acanthometron conicum_, n. sp.

Spines short and thick, conical, gradually thinner from the thick conical

base towards the simple apex. Central part of the base with a large fulcral

pyramid, but without leaf-cross. Central capsule transparent, colourless

(?).

_Dimensions._--Length of the spines 0.08 to 0.12, basal breadth 0.02.

_Habitat._--North Pacific, Station 244, surface.

{744}7. _Acanthometron pellucidum_, J. Müller.

_Acanthometra pellucida_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 47, Taf. xi. figs. 1-3.

_Acanthometra pellucida_, Haeckel, 1862, Monogr. d. Radiol., p. 378.

Spines cylindrical, very thin and long, needle-shaped, nearly of equal

thickness in their whole length. Central base with a small fulcral pyramid,

without leaf-cross. Distal apex bifid or bifurcate, with two thin parallel

teeth. Central capsule pellucid, colourless, with yellow pigment-bodies.

(Differs from _Acanthometron elasticum_ mainly in the bifid apex.)

_Dimensions._--Length of the spine 0.1 to 0.3, breadth 0.002 to 0.004.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

8. _Acanthometron wageneri_, Haeckel.

_Acanthometra wageneri_, Haeckel, 1862, Monogr. d. Radiol., p. 378.

Spines cylindrical, in the thickened outer half about twice as broad as in

the thin inner half. Central base a little thickened, with large fulcral

pyramid, but without leaf-cross. Distal apex bifid, with two divergent,

often denticulated teeth. Central capsule pellucid, with yellow

pigment-bodies. (Differs from _Acanthometron dolichoscion_ mainly in the

bifid apex.)

_Dimensions._--Length of the spines 0.2 to 0.5, breadth in the inner part

0.003, in the outer 0.006.

_Habitat._--Adriatic Sea; Triest, Wagner; Corfu, Haeckel, surface.

Subgenus 2. _Phyllostaurus_, Haeckel, 1862, Monogr. d. Radiol., p. 381.

_Definition._--Spines at the central base with a broad leaf-cross, composed

of four prominent triangular lamellæ; the meeting edges of the neighbouring

lamellæ are propped one upon another in such a manner that there are formed

twenty-two hollow pyramidal spaces or compartments (compare p. 721).

9. _Acanthometron siculum_, Haeckel.

_Acanthometra sicula_, Haeckel, 1862, Monogr. d. Radiol., p. 382, Taf.

xvii. figs. 1, 2; Taf. xviii. fig. 8.

Spines elongate, conical, tapering gradually from the thick base towards

the simple distal apex. Conical circular base supported by a basal

leaf-cross of double the breadth. Central capsule yellowish-brown, opaque.

_Dimensions._--Length of the spines 0.3 to 0.4, basal breadth 0.008 to

0.012, leaf-cross 0.024.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

{745}10. _Acanthometron catervatum_, Haeckel.

_Acanthometra brevispina_, Haeckel, 1862, Monogr. d. Radiol., p. 382,

Taf. xv. fig. 5, Taf. xviii. fig. 9.

Spines cylindrical, nearly of equal breadth throughout their whole length.

Apex either simple, conical, or bifid. Base with a large leaf-cross, four

to six times as broad as the spine itself. Central capsule transparent,

yellow. The Atlantic specimens have much longer spines than those figured

from the Mediterranean, but are otherwise not different. Therefore I have

changed the inconvenient name _brevispinum_ into _catervatum_.

_Dimensions._--Length of the spines 0.1 to 0.3, breadth 0.005 to 0.008;

basal leaf-cross 0.02 to 0.032.

_Habitat._--Mediterranean (Messina); North Atlantic, Station 354, Gulf

Stream (Færöe Channel) in great abundance, John Murray, surface.

Subgenus 3. _Astrolithium_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.

d. Wiss. Berlin, p. 810.

_Definition._--Spines in the basal part grown perfectly together, so that

the whole skeleton forms a single piece of acanthin; a star with twenty

equal rays.

11. _Acanthometron bulbiferum_, n. sp. (Pl. 130, fig. 1).

_Astrolithium bulbiferum_, Haeckel, 1881, Prodromus, p. 466.

Spines needle-shaped, cylindrical, very thin and long, with simple apex;

suddenly thickened and forming a broad regular cone at the central base;

all twenty conical bulbs have their broad bases grown together and forming

a central icosahedron of acanthin; from its twenty faces arise the circular

bases of the cones in regular disposition.

_Dimensions._--Length of the spines 0.2 to 0.5, breadth 0.001 to 0.003;

height of the basal cones 0.06, basal breadth of them 0.02.

_Habitat._--Central Pacific, Stations 265 to 274, surface.

12. _Acanthometron bifidum_, Haeckel.

_Astrolithium bifidum_, Haeckel, 1862, Monogr. d. Radiol., p. 400, Taf.

xx. fig. 5.

Spines needle-shaped, cylindrical, of equal breadth in their whole length.

Distal apex bifid, with two parallel straight teeth. Central bases of all

twenty spines grown perfectly together and forming a central sphere of

acanthin. Central capsule brown opaque.

_Dimensions._--Length of the spines 0.2, breadth 0.003.

_Habitat._--Mediterranean (Messina), Haeckel, surface.

{746}Genus 324. _Zygacantha_,[364] J. Müller, 1858, Abhandl. d. k. Akad. d.

Wiss. Berlin, p. 51.

_Definition._--#Astrolonchida# with simple, compressed, and two-edged

radial spines, without apophyses; their transverse section is elliptical or

rhomboidal.

The genus _Zygacantha_ comprised in the original definition of J. Müller

only a single species, _Zygacantha furcata_, distinguished from the other

#Acanthometra# by forked spines with two long parallel teeth. It seems now

advisable to unite in this genus all those Astrolonchida in which the

simple spines are two-edged, compressed, or leaf-shaped. The term

_Zygacantha_ may be conceived as the general expression of the important

fact, that in all Icosacantha the twenty spines are opposite in pairs.

Subgenus 1. _Zygacantharium_, Haeckel.

_Definition._--Spines at the central base without leaf-cross and without

hollow pyramidal compartments, united by the opposed triangular faces of

their pyramidal bases, resting one upon another.

1. _Zygacantha lanceolata_, Haeckel.

_Acanthometra lanceolata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 48, Taf. xi. fig. 12.

_Acanthometra lanceolata_, Haeckel, 1862, Monogr. d. Radiol., p. 380.

Spines lanceolate, from the broader middle part equally thinned towards the

two ends. Apex simple. Base pyramidal, without leaf-cross. Each flat

lamellar spine exhibits an elevated middle rib (like a lanceolate leaf),

and is therefore compressed quadrangular.

_Dimensions._--Length of the spines 0.1 to 0.15, greatest breadth (in the

width) 0.03 to 0.04.

_Habitat._--Mediterranean (Saint Tropez, French shore), J. Müller; North

Atlantic (Canary Islands), Haeckel, surface.

2. _Zygacantha costata_, n. sp.

Spines compressed, two-edged, linear, of nearly equal breadth in their

whole length. Apex truncate. Base pyramidal, without leaf-cross. Each flat

lamellar spine exhibits an elevated middle rib, which in the distal half is

cleft into two divergent rods ending in the corners of the truncated apex.

(Similar to _Zygacantha dicopa_, but with broader free spines, which are

not grown together in the centre.)

_Dimensions._--Length of the spines 0.1 to 0.15, breadth 0.02.

_Habitat._--Central Pacific, Stations 265 to 274, surface.

{747}3. _Zygacantha compressa_, Haeckel.

_Acanthometra compressa_, Haeckel, 1862, Monogr. d. Radiol., p. 378, Taf.

xviii. figs. 4_a_, 4_b_.

Spines in the proximal half compressed, broad lanceolate, four to six times

as broad as in the thin cylindrical distal half. Apex simple or short

bifid. Base pyramidal, thickened, without leaf-cross. No middle rib.

Central capsule opaque, yellowish or reddish-brown.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth of the inner half

0.015 to 0.02, of the outer half 0.002 to 0.003.

_Habitat._--Mediterranean (Messina); Atlantic (Canary Islands), Station

352, surface.

4. _Zygacantha furcata_, J. Müller.

_Zygacantha furcata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 51, Taf. ix. fig. 6.

_Acanthometra furcata_, J. Müller, 1856, Monatsber. d. k. preuss. Akad.

d. Wiss. Berlin, p. 499.

_Acanthometra furcata_, Haeckel, 1862, Monogr. d. Radiol., p. 380.

Spines compressed, fork-shaped, divided by two thickened knots into three

sections of nearly equal length; middle section broader than the proximal,

but smaller than the distal section, which is cleft by a deep fissure into

two long parallel straight branches. Base pyramidal, without leaf-cross.

Central capsule purple, with yellow bodies.

_Dimensions._--Length of the spines 0.1 to 0.15, basal breadth 0.003 to

0.005, distal breadth 0.02 to 0.03.

_Habitat._--Mediterranean (Cette). J. Müller, surface.

Subgenus 2. _Zygacanthidium_, Haeckel.

_Definition._--Spines at the central base with a cross of four prominent

leaves; the meeting edges of the neighbouring lamellæ so rest one upon

another that twenty-two hollow pyramidal compartments are formed (compare

p. 721).

5. _Zygacantha dichotoma_, Haeckel.

_Zygacantha dichotoma_, Haeckel, 1862, Monogr. d. Radiol., p. 381.

_Acanthometra dichotoma_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 50, Taf. ix. fig. 5.

Spines compressed, pincer-shaped, cleft nearly throughout their whole

length into two thin parallel straight rods or fork branches, which are

united only in their middle by a narrow bridge, and at their central base

by the pyramidal small central apex; above this pyramid each rod is divided

into two broad triangular leaves, forming a large basal leaf-cross. Central

capsule purple, with yellow bodies.

_Dimensions._--Length of the spines 0.1 to 0.15, breadth 0.01 to 0.02.

_Habitat._--Mediterranean (Nice), J. Müller, surface.

{748}6. _Zygacantha complanata_, n. sp.

Spines compressed, two-edged, linear, of equal breadth throughout their

whole length. Apex bifid. Base thickened, with a large leaf-cross. (Similar

to _Amphilonche complanata_, but different in the equal size of all twenty

spines, which are somewhat broader.)

_Dimensions._--Length of the spines 0.12 to 0.18, breadth 0.002.

_Habitat._--North Pacific, Station 244, surface.

7. _Zygacantha semicompressa_, Haeckel.

_Acanthometra hemicompressa_, Car, 1884, Zool. Anzeiger, p. 94, with

woodcut.

Spines in the proximal half compressed, two-edged, linear, three to four

times as broad as in the needle-shaped cylindrical distal half. Apex

simple. Base pyramidal, with a small leaf-cross. Central capsule

transparent.

_Dimensions._--Length of the spines 0.1 to 0.2, breadth in the proximal

half 0.02, in the distal half 0.006.

_Habitat._--Mediterranean (Genoa), Haeckel; Adriatic Sea (Trieste), Car,

surface.

8. _Zygacantha foliacea_, n. sp.

Spines lanceolate, tapering from the broader middle part towards the two

ends, with two dentated or serrated edges and a prominent middle rib. Apex

simple. Base with a small leaf-cross. The spines like the leaves of _Agave

americana_.

_Dimensions._--Length of the spines 0.15 to 0.2, middle breadth 0.02 to

0.03.

_Habitat._--Indian Ocean, near the Island of Socotra, Haeckel.

Subgenus 3. _Zygacanthonium_, Haeckel.

_Definition._--Spines in the centre grown perfectly together and forming a

single star-shaped piece of acanthin.

9. _Zygacantha dicopa_, Haeckel.

_Astrolithium dicopum_, Haeckel, 1862, Monogr. d. Radiol., p. 400, Taf.

xx. figs. 3, 4.

Spines compressed, two-edged, linear, of nearly equal breadth throughout

their whole length, with a prominent middle rib, which in the distal third

is cleft into two divergent teeth, ending in the two corners of the broad,

obliquely truncated apex. All twenty spines with their central bases grown

together and forming one single piece of acanthin--a star with twenty rays.

_Dimensions._--Length of the spines 0.12 to 0.2, breadth 0.01 to 0.02.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, many Stations,

surface.

{749}Genus 325. _Acanthonia_,[365] Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Astrolonchida# with simple, four-edged, prismatic or

pyramidal radial spines, without apophyses; their transverse section is

square.

The genus _Acanthonia_ comprises all those Astrolonchida (formerly united

with _Acanthometron_) in which the simple spines either in their whole

length or in the greatest part of it are four-edged, with square transverse

section. They are sometimes more prismatic (with equal breadth), at other

times more pyramidal (with decreasing breadth towards the distal apex). If

_Acanthometron_ be the common simple ancestral form of the Acanthonida,

then the two-edged _Zygacantha_, and the four-edged _Acanthonia_ may be

regarded as two divergent main lines arising from it; the former leading to

the Phractacanthida and Diporaspida, the latter leading to the

Stauracanthida and Tessaraspida.

Subgenus 1. _Acanthonarium_, Haeckel.

_Definition._--Spines at the central base, without leaf-cross and without

hollow pyramidal compartments, united by the triangular faces of their

pyramidal bases, resting one upon another.

1. _Acanthonia tetracopa_, Haeckel (Pl. 129, figs. 9-11).

_Acanthometra tetracopa_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 47, Taf. vii. figs. 3 to 5, Taf. xi. fig. 5.

_Acanthometra tetracopa_, Haeckel, 1862, Monogr. d. Radiol., p. 379, Taf.

xviii. fig. 5.

Spines quadrangular prismatic, with prominent lamellar edges, of equal

breadth in their whole length. Base pyramidal, without leaf-cross. Apex

truncated, or with four short teeth (sometimes only two teeth). Central

capsule opaque, brown or yellow.

_Dimensions._--Length of the spines 0.15 to 0.2, breadth 0.01 to 0.012.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, many

Stations, surface.

2. _Acanthonia prismatica_, n. sp.

Spines quadrangular prismatic, without prominent edges, with four plane

lateral faces, of equal breadth throughout their whole length. Base

pyramidal, without leaf-cross. Apex truncate, with square apical face.

_Dimensions._--Length of the spines 0.1 to 0.16, breadth 0.005 to 0.008.

_Habitat._--Antarctic Ocean, Station 154, surface.

{750}3. _Acanthonia denticulata_, n. sp.

Spines quadrangular prismatic, with prominent elegantly denticulated edges,

of equal breadth throughout their whole length. Both ends pyramidal,

without leaf-cross. (Similar to _Amphilonche denticulata_, but with the

twenty spines all equal, and with spherical central capsule.)

_Dimensions._--Length of the spines 0.12 to 0.16, breadth 0.008.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

4. _Acanthonia mülleri_, Haeckel.

_Acanthometra mülleri_, Haeckel, 1862, Monogr. d. Radiol., p. 379, Taf.

xv. fig. 3, Taf. xviii. fig. 6.

Spines quadrangular, nearly prismatic, but tapering gradually from the

pyramidal base towards the distal bifid apex, which bears two thin,

parallel, or little divergent teeth; four edges elegantly denticulated;

base without leaf-cross. Central capsule yellowish or reddish.

_Dimensions._--Length of the spines 0.12 to 0.18, basal breadth 0.005.

_Habitat._--Mediterranean (Messina); Atlantic, Stations 348 to 352,

surface.

5. _Acanthonia fragilis_, Haeckel.

_Acanthometra fragilis_, Haeckel, 1862, Monogr. d. Radiol., p. 380, Taf.

xv. fig. 4, Taf. xviii. fig. 7.

Spines quadrangular, nearly prismatic, but gradually thickened from the

pyramidal base towards the distal truncated end; four edges regularly

denticulated; base without leaf-cross. Central capsule opaque.

_Dimensions._--Length of the spines 0.5 and more, basal breadth 0.002 to

0.003, distal breadth 0.008 to 0.016 or more.

_Habitat._--Mediterranean (Messina); North Atlantic, Station 354, surface.

6. _Acanthonia convexa_, n. sp.

Spines quadrangular, with four broad lamellar, convex, prominent edges,

which from the broader middle part are thinned towards the two emarginated

ends; each end with a small quadrangular pyramid, without leaf-cross. All

the twenty spines of this species exhibit nearly the same form, which is

seen in the caudal or posterior (geotomical) spine of _Amphilonche anomala_

(Monogr. d. Radiol., Taf. xviii. fig. 23, _b_).

_Dimensions._--Length of the spines 0.12 to 0.16, breadth in the middle

part 0.02 to 0.025.

_Habitat._--North Pacific, Station 244, surface.

7. _Acanthonia concava_, n. sp.

Spines quadrangular, with four broad lamellar, concave, prominent edges,

which from the smaller middle part are broadened towards the two

emarginated ends; each end with a small {751}quadrangular pyramid, without

leaf-cross. All the twenty spines of this species exhibit nearly the same

form, which is seen in the frontal or anterior (hydrotomical) spine of

_Amphilonche anomala_ (Monogr. d. Radiol., Taf. xviii. fig. 23, _a_).

_Dimensions._--Length of the spines 0.15, breadth in the middle part 0.012,

on both ends 0.025.

_Habitat._--South Pacific, Station 288, surface.

8. _Acanthonia quadrangula_, n. sp.

Spines quadrangular prismatic, with smooth prominent straight edges, but of

very different breadth in both halves; the inner or proximal half (inside

the central capsule) twice to four times as broad as the outer or distal

half (outside the central capsule); both ends suddenly separated by a

constriction, in which is inserted the membrane of the capsule. The latter

is pellucid, with a number of yellow bodies. Apex of the spines simple,

base pyramidal, without leaf-cross.

_Dimensions._--Length of the spines 0.2 to 0.4, breadth of the basal half

0.01, of the distal half 0.002 to 0.004.

_Habitat._--Atlantic, Canary Islands, Azores, Station 354, surface.

Subgenus 2. _Acanthonidium_, Haeckel.

_Definition._--Spines at the central base with a broad leaf-cross, composed

of four prominent triangular lamellæ; the meeting edges of these crossed

lamellæ between every three or four neighbouring spines so rest one upon

another that twenty-two hollow pyramidal compartments are formed (compare

p. 721).

9. _Acanthonia echinoides_, Haeckel.

_Acanthometra echinoides_, Claparède et Lachmann, 1858, Études sur les

Infusoires et les Rhizopodes, &c., p. 459, pl. xxiii. figs. 1-5.

_Acanthometra echinoides_, Haeckel, 1862, Monogr. d. Radiol., p. 383.

Spines quadrangular prismatic without prominent edges, with four plane

lateral faces, of equal breadth throughout their whole length. Central

base three to four times as broad, with large leaf-cross. Apex truncated or

bifid (sometimes with four short teeth).

_Dimensions._--Length of the spines 0.3 to 0.5, breadth 0.004 to 0.008;

leaf-cross 0.02 to 0.03.

_Habitat._--North Atlantic, west coast of Norway (Claparède et Lachmann);

Færöe Channel (Gulf Stream), John Murray, surface.

10. _Acanthonia claparedei_, Haeckel.

_Acanthometra claparedei_, Haeckel, 1862, Monogr. d. Radiol., p. 383,

Taf. xviii. fig. 12.

Spines quadrangular prismatic, with four prominent lamellar edges, of equal

breadth throughout their whole length. Apex bifid. Central base twice as

broad, with large leaf-cross. Central capsule opaque, reddish-brown.

_Dimensions._--Length of the spines 0.6, breadth 0.016; leaf-cross 0.032.

_Habitat._--Mediterranean (Messina); Atlantic, Station 347, surface.

{752}11. _Acanthonia cuspidata_, Haeckel.

_Acanthometra cuspidata_, Haeckel, 1862, Monogr. d. Radiol., p. 383, Taf.

xviii. fig. 11.

Spines quadrangular pyramidal, with four prominent lamellar edges, tapering

gradually from the broad base towards the simple distal apex. Basal

leaf-cross as broad, with a small central pyramid.

_Dimensions._--Length of the spines 0.5, basal breadth 0.012; leaf-cross

0.025.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

12. _Acanthonia quadrifolia_, Haeckel.

_Acanthometra quadrifolia_, Haeckel, 1862, Monogr. d. Radiol., p. 382,

Taf. xviii. fig. 10.

Spines in the basal part quadrangular pyramidal, with four prominent

lamellar edges and a large basal leaf-cross; in the distal part three to

six times as long, cylindrical, of equal breadth. Apex simple, conical, or

bifid. Central capsule yellow or whitish. This common species differs from

the nearly allied _Acanthometron catervatum_ mainly by the strong

development of the large basal leaves or wings.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth in the distal half

0.002, in the basal part 0.02.

_Habitat._--Mediterranean; North Atlantic, Stations 252 to 254; Færöe

Channel, Gulf Stream, in enormous numbers, John Murray, surface and at

various depths.

13. _Acanthonia diplopyramis_, n. sp.

Spines formed like a quadrangular double pyramid or an irregular

octahedron; the basal leaf-cross being extremely developed, with four very

large and thin lamellar leaves; the basal halves of the twenty double

pyramids are united by the meeting edges of those leaves, while their

distal halves are free, with simple apices. Therefore the four triangular

leaves of each spine are equally thinned from the middle towards the two

ends.

_Dimensions._--Length of the spines 0.1 to 0.2, greatest breadth 0.04 to

0.08.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

14. _Acanthonia multispina_, Haeckel.

_Acanthometra multispina_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 47, Taf. vii. figs. 6-9.

_Acanthometra multispina_, Haeckel, 1862, Monogr. d. Radiol., p. 384.

Spines quadrangular, with four lamellar prominent edges, in the proximal

half nearly prismatic, in the distal half pyramidal; both halves separated

by a prominent short tooth on each edge. Here in the middle part the

breadth (including the four teeth) is equal to the basal leaf-cross.

Central capsule opaque, brown.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth 0.01 to

0.02.

_Habitat._--Mediterranean (Messina); Tropical Atlantic, Station 348.

{753}15. _Acanthonia serrulata_, n. sp.

Spines quadrangular pyramidal, with simple apex; the large basal leaf-cross

nearly half as long as the prolonged distal part. The four prominent

triangular edges of the latter are very thin and broad lamellæ, finely

dentate or serrate.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth 0.05 to

0.06.

_Habitat._--Central Pacific, Station 272, surface.

Subgenus 3. _Acantholithium_, Haeckel.

_Definition._--Spines in the basal part grown together, so that the whole

skeleton is not composed of twenty separated pieces, but represents a

single piece of acanthin--a star with twenty equal rays.

16. _Acanthonia stellata_, n. sp.

Spines quadrangular pyramidal, with simple distal apex, in the basal part

grown perfectly together, so that the whole skeleton forms a single piece

of acanthin--a starlet with twenty equal rays. The free pyramidal part of

each spine is twice to four times as long as the basal part.

_Dimensions._--Length of the spines 0.1 to 0.15, greatest breadth (on the

surface of the central solid sphere) 0.02 to 0.04.

_Habitat._--Central Pacific, Station 271, surface.

Subfamily 2. PHRACTACANTHIDA, Haeckel.

_Definition._--#Astrolonchida# with twenty radial spines, each of which

bears two opposite apophyses or lateral transverse processes; sometimes two

longitudinal rows of opposite apophyses.

Genus 326. _Lithophyllium_,[366] J. Müller, 1858, Abhandl. d. k. Akad. d.

Wiss. Berlin, p. 52.

_Definition._--#Astrolonchida# with two simple, not branched, opposite

apophyses on each radial spine.

The genus _Lithophyllium_ was founded by J. Müller for a single species

(_Lithophyllium foliosum_), which we also here retain as the type of the

genus. It is the first observed Astrolonchid, which bears two opposite

lateral apophyses on each spine, and may therefore be regarded as the

ancestral form of the subfamily Phractacanthida. The two opposite apophyses

are here simple, whilst in the other genera of the subfamily they are

branched or multiplied.

{754}1. _Lithophyllium cruciatum_, Haeckel.

_Acanthometra cruciata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 49, Taf xi. fig. 11.

_Xiphacantha cruciata_, Haeckel, 1862, Monogr. d. Radiol., p. 385, Taf.

xviii. fig. 13.

Spines cylindrical, very thin, crossed perpendicularly in the distal third

by a thin transverse beam; both lateral rods of the cross have the same

length as the distal end. Apex simple. Base pyramidal, without leaf-cross.

_Dimensions._--Length of the spines 0.05 to 0.15, breadth 0.001 to 0.002.

_Habitat._--Mediterranean, Atlantic, Stations 352 to 354, &c., surface.

2. _Lithophyllium gladiatum_, n. sp. (Pl. 130, fig. 3).

Spines compressed, sword-shaped, two-edged, crossed perpendicularly in the

middle part by a broad, somewhat curved transverse beam; both lateral rods

of the cross are triangular compressed, and have the same length as the

proximal end. Apex simple. Base pyramidal, without leaf-cross.

_Dimensions_.--Length of the spines 0.2 to 0.25, breadth 0.01.

_Habitat_.--North Pacific, Station 241, surface.

3. _Lithophyllium condylatum_, n. sp.

Spines compressed quadrangular, tapering from the broader middle towards

the two ends; from the middle part arise two opposite perpendicular

apophyses, which bear on the rounded end a thickened condyle. Apex simple.

Base pyramidal, with a small leaf-cross.

_Dimensions._--Length of the spines 0.1 to 0.12, breadth in the middle part

0.02.

_Habitat._--Central Pacific, Station 266 to 272, surface.

4. _Lithophyllium foliosum_, J. Müller.

_Lithophyllium foliosum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 52, Taf. xi. figs. 6-10.

_Xiphacantha foliosa_, Haeckel, 1862, Monogr. d. Radiol., p. 385.

Spines lanceolate, tapering from the broader middle towards the two ends.

From the middle part or from the outer third arise two opposite triangular

apophyses, which are not perpendicular to the axis of the spine, but form

an acute angle with its distal part. Therefore each spine represents a

broad leaf with a middle rib and with three lobes or truncated teeth. The

distal apex is distinguished by a violet colour. Base pyramidal, without

leaf-cross. Central capsule yellow.

_Dimensions._--Length of the spines 0.05 to 0.1, breadth 0.02 to 0.03.

_Habitat._--Mediterranean, French shore, Saint Tropez, J. Müller.

{755}Genus 327. _Phractacantha_,[367] Haeckel, 1881, Prodromus, p. 465.

_Definition_.--#Astrolonchida# with two branched, but not latticed,

opposite apophyses on each radial spine.

The genus _Phractacantha_ differs from its ancestral form, the preceding

_Lithophyllium_ by the ramification of the apophyses, which are either

forked or bear lateral branches. If the prolonged fork-branches of the

neighbouring spines meet and form a lattice-shell, this genus passes over

into _Phractaspis_, the common ancestral form of the Diporaspida.

1. _Phractacantha_ bifurca, n. sp.

Spines cylindrical, thin, of equal breadth throughout their whole length.

Apex simple. Base pyramidal, without leaf-cross. From the outer third arise

two opposite, thin, forked apophyses; ends of the fork branches acute.

_Dimensions._--Length of the spines 0.1, breadth 0.006.

_Habitat._--Central Pacific, Station 274, surface.

2. _Phractacantha bipennis_, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the

two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle

arise two opposite broad, forked apophyses; ends of the fork-branches broad

and obtuse.

_Dimensions._--Length of the spines 0.15, breadth in the middle 0.012.

_Habitat._--Central Pacific, Station 266, surface.

Genus 328. _Doracantha_,[368] Haeckel, 1881, Prodromus, p. 465.

_Definition_.--#Astrolonchida# with two latticed or fenestrated apophyses

on each radial spine.

The genus _Doracantha_ arises from the foregoing _Phractacantha_ by union

of the fork-branches of the apophyses on each spine. By this concrescence

is formed a polygonal or roundish plate with two pores, pierced by the

radial spine between them. _Doracantha_ may be regarded as a _Dorataspis_,

in which the twenty small fenestrated plates have not become united.

{756}1. _Doracantha dorataspis_, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the

two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle

part of each spine arise two opposite forked apophyses; the neighbouring

fork-branches are recurved and united in the tangential plane; so that each

spine bears a plate or shield with two elliptical pores; the margin of the

roundish plate bears a variable number of short teeth.

_Dimensions._--Length of the spines 0.2, breadth 0.02.

_Habitat._--Central Pacific, Station 271, surface.

Genus 329. _Astrolonche_,[369] Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Astrolonchida# with numerous simple apophyses (four to

eight or more on each radial spine), which are arranged in two opposite

longitudinal rows (rarely in six such rows, opposite in three parallel

planes).

The genus _Astrolonche_ differs from the preceding Phractacanthida in the

multiplication of the simple apophyses. Commonly these are opposite in

pairs in two longitudinal rows (on the two edges of the compressed spine,

at least two on each side). But sometimes (in the subgenus

_Astrolonchidium_) there are six instead of two longitudinal rows of teeth,

and these are placed in three parallel planes.

Subgenus 1. _Astroloncharium_, Haeckel.

_Definition._--Each spine with two longitudinal rows of apophyses, opposite

in one meridian plane.

1. _Astrolonche bicruciata_, n. sp.

Spines compressed, two-edged, almost of equal breadth throughout their

whole length, with simple apex and small leaf-cross at the base. From the

two edges of the middle part of each spine arise two pairs of opposite

apophyses, which are compressed and a little curved (convex on the distal,

concave on the proximal margin). All four apophyses are of the same size

and form; the radial distance of each pair much smaller than their common

distance from the centre.

_Dimensions._--Length of the spines 0.25, breadth 0.02.

_Habitat._--Central Pacific, Station 270, surface.

2. _Astrolonche mucronata_, Haeckel.

_Acanthometra mucronata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 49, Taf. x. fig. 9.

_Aspidomma mucronatum_, Haeckel, 1862, Monogr. d. Radiol., p. 424.

Spines conical, little compressed, with simple apex and small leaf-cross at

the base. From the basal half of each spine arise two pairs of opposite

apophyses, which exhibit a very different form. {757}The upper or distal

apophyses (nearly in the middle of the spine) are flat, leaf-shaped,

broadened in the periphery, often lobed, and sometimes branched or even

fenestrated. (Transition to _Phractaspis_ and _Dorataspis_, or to

_Phractopelta_?) The lower or proximal apophyses are thick, simple, all

slightly curved; they are equidistant from the former and from the centre.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth 0.01.

_Habitat._--Mediterranean (Cette on the French shore), surface, J. Müller.

3. _Astrolonche pectinata_, Haeckel.

_Acanthometra pectinata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 48, Taf. x. figs. 1, 2.

_Xiphacantha pectinata_, Haeckel, 1862, Monogr. d. Radiol., p. 386.

Spines compressed quadrangular, with short, simple or bifid apex, pyramidal

on the base, without leaf-cross. From the two broader edges of the proximal

half arise two longitudinal rows of opposite apophyses; three to four

slender teeth in each row.

_Dimensions._--Length of the spines 0.2, breadth 0.08.

_Habitat._--Mediterranean, Cette (French shore), surface, J. Müller.

4. _Astrolonche pinnata_, n. sp.

Spines in the distal half compressed, linear, two-edged, with bifid apex;

in the proximal half three times as broad lanceolate, at the base

pyramidal, without leaf-cross. From the two broader edges of the proximal

half arise two longitudinal rows of opposite apophyses; four to six broad

triangular teeth in each row.

_Dimensions._--Length of the spines 0.3 to 0.4, breadth in the outer half

0.012, in the inner half 0.03 to 0.04.

_Habitat._--South Atlantic, Station 332, surface.

Subgenus 2. _Astrolonchidium_, Haeckel.

_Definition._--Each spine with three parallel double rows of opposite

apophyses.

5. _Astrolonche serrata_, Haeckel.

_Xiphacantha serrata_, Haeckel, 1862, Monogr. d. Radiol., p. 386, Taf.

xvii. fig. 3, Taf. xviii. figs. 14_a_, 14_b_.

_Xiphacantha serrata_, R. Hertwig, 1879, Organismus d. Radiol., p. 11,

Taf. ii. fig. 4.

_Acanthometra serrata_, Haeckel, 1860, Monogr. d. Radiol., p. 807.

Spines in the distal half thin, nearly cylindrical or a little compressed,

thinned towards the short simple or bifid apex; in the proximal half three

to six times as broad, four-winged, with six longitudinal rows of opposite

apophyses. From the edges of the two broader (lateral) wings arise three

{758}to four pairs of strong conical teeth; from the edges of the two

smaller (sagittal) wings arise also three to four pairs of teeth, but very

short and broad, triangular; each of these teeth bears on both its

(lateral) sides two opposite slender conical teeth, which are parallel to

the large conical teeth of the lateral wings. Therefore all teeth (eighteen

to twenty-four) are placed opposite in pairs in three parallel planes. Base

of the spines pyramidal, with a small leaf-cross. The central capsule of

this large and very remarkable species commonly entirely includes the

apophyses of the spines, and is opaque, whitish.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth of the distal half

0.002 to 0.004, of the proximal half 0.01 to 0.02.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

Subfamily 3. STAURACANTHIDA, Haeckel.

_Definition._--#Astrolonchida# with a cross of four free apophyses (or four

crossed longitudinal rows of apophyses) on each radial spine.

Genus 330. _Xiphacantha_,[370] Haeckel, 1862, Monogr. d. Radiol., p. 384.

_Definition._--#Astrolonchida# with four simple apophyses on each radial

spine, opposite in pairs in the form of a cross.

The genus _Xiphacantha_ was founded by me in 1862 for all those

_Acanthometrida_ which bear simple or branched apophyses on their twenty

equal spines. I restrict here the genus to those Astrolonchida which bear

on each spine a cross of four simple, not branched, apophyses. These are

either conical teeth or broad wings, sometimes extremely thin leaves.

_Xiphacantha_ may be regarded as the ancestral form not only of the

subfamily Stauracanthida, but also of the Tessaraspida, derived from the

latter.

Subgenus 1. _Xiphacanthonia_, Haeckel.

_Definition._--Apophyses of the radial spines small, formed like a tooth or

a hook, not wing-shaped. Edges of the spines commonly narrow, little

prominent.

1. _Xiphacantha quadridentata_, Haeckel.

_Xiphacantha quadridentata_, Haeckel, 1862, Monogr. d. Radiol., p. 387,

Taf. xviii. figs. 15_a_, 15_b_.

_Acanthometra quadridentata_, J. Müller, 1858, Abhandl. d. k. Akad. d.

Wiss. Berlin, p. 48, Taf. x. fig. 3.

Spines slender, four-sided prismatic, gradually thinner towards the simple

pyramidal apex. Base with large wing-cross. Four apophyses about in the

middle of each spine, conical, straight, smooth, about as long as the basal

breadth of the spine. Central capsule opaque, reddish-brown.

{759}_Dimensions._--Length of the spines 0.2 to 0.3, breadth in the middle

part 0.012, on the base 0.02; length of the apophyses 0.02 to 0.03.

_Habitat._--Mediterranean, Atlantic, Stations 348, 354, surface.

2. _Xiphacantha crucifera_, n. sp.

Spines slender, four-sided prismatic, thin, of nearly equal breadth

throughout the whole length. Base with small wing-cross. Four apophyses

much nearer the proximal than the distal end, thin, straight smooth, three

to six times as long as the basal breadth of the spine. Central capsule

pellucid, with yellow bodies.

_Dimensions._--Length of the spines 0.4 to 0.5, breadth 0.002 to 0.004;

length of the apophyses 0.01 to 0.02.

_Habitat._--Central Pacific, Station 266, surface.

3. _Xiphacantha spinulosa_, Haeckel.

_Xiphacantha spinulosa_, Haeckel, 1862, Monogr. d. Radiol., p. 388, Taf.

xvii. fig. 4.

_Acanthometra spinulosa_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.

d. Wiss. Berlin, p. 807.

Spines stout, four-sided prismatic, of nearly equal breadth throughout the

whole length, on the distal apex truncated, two-edged. Base with large

wing-cross. Four apophyses about in the middle of each spine, conical,

straight, spinulated, twice to four times as long as the basal breadth of

the spine. Central capsule opaque, yellow.

_Dimensions._--Length of the spines 0.27, breadth 0.014; length of the

apophyses 0.05.

_Habitat._--Mediterranean (Messina), surface.

4. _Xiphacantha emarginata_, n. sp.

Spines stout, four-sided, in the proximal half prismatic, in the distal

half pyramidal, with emarginated apex. Base with very large wing-cross.

Four apophyses about in the middle of each spine, compressed, straight,

two-edged, with emarginated ends, about twice as long as the basal breadth

of the spine. Central capsule small, pellucid.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth 0.02 to 0.03;

length of the apophyses 0.04 to 0.06.

_Habitat._--South Pacific, Station 291, surface.

5. _Xiphacantha falcata_, n. sp.

Spines slender, four-sided prismatic, gradually thickened from both ends

towards the middle part, with simple apex. Base with very small wing-cross.

Four apophyses about in the middle part of each spine, falcated,

compressed, recurved, twice to three times as long as the greatest breadth

of the spine.

{760}_Dimensions._--Length of the spines 0.3 to 0.4, greatest breadth

0.015; length of the apophyses 0.03 to 0.05.

_Habitat._--Central Pacific, Station 270, surface.

6. _Xiphacantha ancorata_, n. sp.

Spines slender, four-sided prismatic, gradually thickened from the narrow

base towards the short, simple, pyramidal apex. Base with large wing-cross.

Four apophyses on the distal end, immediately below the pyramidal apex,

falcated, strongly recurved, like an anchor with four strong teeth.

_Dimensions._--Length of the spines 0.4 to 0.5, basal breadth 0.005, distal

breadth 0.015; length of the apophyses 0.04.

_Habitat._--Indian Ocean, Madagascar, Rabbe.

Subgenus 2. _Xiphacanthidium_, Haeckel.

_Definition._--Apophyses of the radial spines broad, compressed,

wing-shaped, formed like a large thin plate. Edges of the spines commonly

broad, strongly prominent.

7. _Xiphacantha stauroptera_, n. sp.

Spines four-winged, from the middle part little thinner towards both ends.

Apex simple pyramidal. Base with small wing-cross. Four apophyses

wing-shaped, isosceles triangular or truncated quadrangular; their base is

about half as broad as their length, and occupies in the basal half of each

spine about one-sixth to one-eighth of its length.

_Dimensions._--Length of the spines 0.1 to 0.15; greatest breadth (diagonal

of the cross of the apophyses) 0.006 to 0.009.

_Habitat._--South Atlantic, Station 332, surface.

8. _Xiphacantha trigonoptera_, n. sp.

Spines four-winged, tapering rapidly from the broad middle part towards

both ends. Apex simple pyramidal. Base with a small wing-cross. Four

apophyses equilateral triangular; their base occupies the middle of each

spine, extending to about one-fifth of its length.

_Dimensions._--Length of the spines 0.15 to 0.2, greatest breadth (diagonal

of the cross of the apophyses) 0.06 to 0.08.

_Habitat._--Central Pacific, Station 272, surface.

9. _Xiphacantha macroptera_, n. sp.

Spines four-winged, from the broad middle part gradually thinner towards

both ends. Apex simple pyramidal. Base with small wing-cross. Four

apophyses wing-shaped, very long and broad, {761}triangular; their base

occupies about the middle third of each spine; the proximal side of each

wing is the shortest, truncated or concave.

_Dimensions._--Length of the spines 0.4 to 0.5, greatest breadth (diagonal

of the middle leaf-cross) 0.08 to 0.12.

_Habitat._--North Pacific, Stations 253 to 256, surface.

10. _Xiphacantha platyptera_, n. sp.

Spines four-winged, nearly prismatic in the basal and distal parts. Apex

truncated. Base with small wing-cross. Four apophyses wing-shaped, very

broad and thin, extremely delicate, of irregular quadrangular or nearly

rhomboidal form; their base occupies the middle half of the length of the

spines (second and third quarter). Very variable in form. Often the edges

of the wing-apophyses of the neighbouring spines seem to meet.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth (diagonal

of the leaf-cross) 0.06 to 0.08.

_Habitat._--Pacific, widely distributed, Stations 239, 253, 272, 288, &c.,

surface.

11. _Xiphacantha ciliata_, n. sp. (Pl. 129, figs. 4, 5).

Spines four-winged, prismatic in the basal and the distal third. Apex

pyramidal, short. Base with large leaf-cross. Four apophyses wing-shaped,

nearly semicircular, with dentated edges and rough spinulate or porous

faces; their base occupies the middle third of the length of each spine.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth (diagonal

of the apophysial cross) 0.08 to 0.12.

_Habitat._--Tropical Atlantic, Stations 342 to 352, surface.

12. _Xiphacantha alata_, Haeckel.

_Xiphacantha alata_, Haeckel, 1862, Monogr. d. Radiol., p. 388.

_Acanthometra alata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.

Berlin, p. 48, Taf. ix. figs. 1-3.

Spines four-winged, prismatic in the basal quarter, more slender in the

distal half. Apex simple pyramidal. Base with small wing-cross. Four

apophyses wing-shaped, nearly semicircular, with denticulated edges (and

often also with spinulate faces); their base occupies the second quarter of

the length of each spine.

_Dimensions._--Length of the spines 0.3 to 0.4, greatest breadth (diagonal

of the apophysial cross) 0.05 to 0.06.

_Habitat._--Mediterranean (Nice), Müller, (Portofino), Haeckel.

Genus 331. _Stauracantha_,[371] Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Astrolonchida# with four branched (but not latticed)

apophyses on each radial spine, opposite in pairs in the form of a cross.

{762}The genus _Stauracantha_ differs from its ancestral form,

_Xiphacantha_, in the ramification of the four crossed apophyses on each

spine. These bear either lateral branches, which are parallel to the cross

axes of the radial spine itself (subgenus _Stauracanthonium_), or they are

forked, with divergent branches not parallel to those cross axes (subgenus

_Stauracanthidium_). Both subgenera may perhaps be better separated as

genera. They form the transition to the _Stauraspida_.

Subgenus 1. _Stauracanthonium_, Haeckel.

_Definition._--Apophyses of the radial spines not forked, but crossed by

perpendicular branches, which are placed in tangential planes and parallel

to the cross axes of the quadrangular spine itself.

1. _Stauracantha orthostaura_, n. sp. (Pl. 130, fig. 5).

Spines four-sided prismatic, with simple apex and small leaf-cross at the

base; with four thin slender conical apophyses in the proximal third. Each

apophysis represents a regular rectangular cross, being intersected in its

middle by one perpendicular rod of its own length.

_Dimensions._--Length of the spines 0.3, breadth 0.02; distance of the

apophyses from the apex 0.15 to 0.2.

_Habitat._--South Pacific, Station 169, surface.

2. _Stauracantha tetrastaura_, n. sp.

Spine four-winged prismatic, with four broad prominent edges, pyramidal

apex, and large basal leaf-cross, with four broad compressed apophyses

about in the middle. Each apophysis represents a vertical lamella (placed

in a meridian) with convex distal and concave proximal edge, and is crossed

in its apical part by one perpendicular short rod.

_Dimensions._--Length of the spines 0.5, breadth 0.03; distance of the

apophyses from the centre 0.2.

_Habitat._--Central Pacific, Station 272, surface.

3. _Stauracantha diplostaura_, n. sp.

Spines four-sided prismatic, with truncated apex and broad basal

leaf-cross; in the proximal half with four slender conical apophyses. Each

apophysis is crossed in its apical half at right angles by two short

parallel transverse rods.

_Dimensions._--Length of the spines 0.32, breadth 0.012; distance of the

apophyses from the centre 0.11.

_Habitat._--South Pacific, Station 291, surface.

{763}4. _Stauracantha scalaris_, n. sp.

Spines four-winged prismatic, with four broad prominent edges, truncated

apex, and small basal leaf-cross; in the proximal third with four

compressed lamellar apophyses. Each apophysis is pinnate with opposite

pinnulæ, or crossed at right angles by three to six parallel transverse

rods.

_Dimensions._--Length of the spines 0.24, breadth 0.016; central distance

of the apophyses 0.12.

_Habitat._--Indian Ocean (Madagascar), Rabbe, surface.

5. _Stauracantha johannis_, n. sp. (Pl. 132, fig. 11).

Spines four-sided pyramidal, with simple apex and broad basal leaf-cross,

with four large conical apophyses about in their middle. Each apophysis

bears two irregular rows of alternating perpendicular lateral branches, the

length of which decreases from the base towards the apex of the apophysis.

_Dimensions._--Length of the spines 0.2, middle breadth 0.02; central

distance of the apophyses 0.1.

_Habitat._--South-east Pacific (off Juan Fernandez), Station 300, surface.

6. _Stauracantha murrayana_, Haeckel.

_Xiphacantha species_, Wyville Thomson, 1877, The Atlantic, vol. i. p.

235, fig. 53.

_Xiphacantha murrayana_, Haeckel, 1878, Protistenreich, p. 45, fig. 33.

Spines quadrangular prismatic, with pyramidal apex and small basal

leaf-cross, with four regular conical apophyses in the proximal part. Each

apophysis is crossed at right angles by two parallel transverse rods; the

smaller apical rod is simple; the larger basal rod is crossed again on each

side by a secondary perpendicular branch, which therefore is parallel to

the apophysis itself.

_Dimensions._--Length of the spines 0.3, breadth 0.01, distance of the

apophyses 0.08.

_Habitat._--South Atlantic, Station 332, surface.

7. _Stauracantha pinnulata_, n. sp.

Spines four-winged pyramidal, with prominent edges, simple apex and large

basal leaf-cross, in the middle with doubly pinnate triangular apophyses.

Each apophysis is crossed at right angles by three to four transverse

parallel rods, which bear again perpendicular secondary branches; the

outline of the doubly pinnate apophysis is an isosceles triangle.

_Dimensions._--Length of the spines 0.3, middle breadth 0.02; distance of

the apophyses 0.12.

_Habitat._--North Pacific, Station 244, surface.

{764}Subgenus 2. _Stauracanthidium_, Haeckel.

_Definition._--Apophyses of the radial spines forked, each with two

divergent terminal branches, which are not parallel to the cross axes of

the quadrangular spine.

8. _Stauracantha stauraspis_, Haeckel.

_Dorataspis polyancistra, juvenis_, Haeckel, 1862, Monogr. d. Radiol., p.

418, Taf. xxi. fig. 7.

Spines slender, quadrangular prismatic, with simple apex and pyramidal base

(without basal leaf-cross); with four slender apophyses, which are simply

forked in the outer third. Each apophysis with two recurved fork branches.

_Dimensions._--Length of the spines 0.12, breadth 0.004; distance of the

apophyses 0.06.

_Habitat._--Mediterranean (Messina), surface.

9. _Stauracantha bifurca_, n. sp.

Spines stout, four-winged prismatic, with pyramidal apex and pyramidal base

(without leaf-cross); in their middle with four compressed, little curved

apophyses (convex on the outer, concave on the inner edge), which are

simply forked at the end. Each apophysis with two short straight fork

branches.

_Dimensions._--Length of the spines 0.2, breadth 0.006; distance of the

apophyses 0.08.

_Habitat._--Central Pacific, Station 266, surface.

10. _Stauracantha quadrifurca_, n. sp. (Pl. 130, fig. 4).

Spines slender, four-sided prismatic, with simple apex and pyramidal base

(without leaf-cross); with four slender apophyses, which are doubly forked

about in their middle. Each apophysis with four short and thin terminal

branches.

_Dimensions._--Length of the spines 0.2, breadth 0.002; distance of the

apophyses from the centre 0.08.

_Habitat._--South Atlantic, Stations 325 to 330, surface.

Genus 332. _Phatnacantha_,[372] Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Astrolonchida# with four apophyses on each radial spine,

opposite in pairs in cross form, and forming a lattice-plate by

communicating branches.

The genus _Phatnacantha_ has been derived from the preceding _Stauracantha_

by concrescence of the branches of the apophyses. Therefore each spine

bears a lattice-plate or a fenestrated shield. If the growing plates of the

neighbouring spines {765}meet together, then the characteristic

lattice-shell of the Tessaraspida is perfect. Either each plate bears four

crossed pores (like _Tessaraspis_), or a larger number of pores (four

aspinal and four to eight or more coronal) like _Icosaspis_.

1. _Phatnacantha tessaraspis_, n. sp.

Spines quadrangular prismatic, with simple pyramidal apex and small basal

leaf-cross. Each spine bears in the basal half a square plate, which is

perforated by four square pores; margin of the plate with twelve short

straight teeth.

_Dimensions._--Length of the spines 0.12, breadth 0.005.

_Habitat._--Central Pacific, Station 265, surface.

2. _Phatnacantha icosaspis_, n. sp. (Pl. 130, fig. 6).

Spines quadrangular with prominent edges; prismatic in the basal half, with

a broad basal leaf-cross, pyramidal in the distal half, with a simple or

truncate apex. Each spine bears in the middle part a square plate, which is

perforated by eight to sixteen or more square pores (four aspinal and four

to eight or more coronal); margin of the plate with twenty-four to

forty-eight or more short straight irregular compressed teeth.

_Dimensions._--Length of the spines 0.18, breadth 0.008.

_Habitat._--Central Pacific, Station 273, surface.

Genus 333. _Pristacantha_,[373] n. gen.

_Definition._--#Astrolonchida# with numerous simple apophyses (eight to

sixteen or more on each radial spine) which are arranged in four

longitudinal rows opposite in pairs in the form of a cross.

The genus _Pristacantha_ differs from all other Stauracanthida in the

multiplication of the crossed apophyses (at least eight on each spine), and

exhibits therefore to them the same relation as _Astrolonche_ exhibits to

the other Phractacanthida. The remarkable _Astrolonchidium serratum_

appears intermediate between both groups.

1. _Pristacantha octodon_, n. sp. (Pl. 130, fig. 9).

Spines four-sided prismatic, a little broader in the middle part than at

either end, with thin prominent edges. Apex truncate or pyramidal. Base

pyramidal, with a small leaf-cross. From the four edges arise in the basal

half (between first and second third of the length) eight slender, conical,

or triangular apophyses (two on each edge).

_Dimensions._--Length of the spines 0.4 to 0.6, breadth 0.02 to 0.04.

_Habitat._--Central Pacific, Station 271, surface.

{766}2. _Pristacantha dodecodon_, n. sp. (Pl. 130, fig. 8).

Spines four-winged, of lanceolate outline, tapering from the broader middle

towards the two ends. Apex pyramidal. Base with a large leaf-cross. From

the four wings arise in the basal part (between first and second third of

the length) twelve triangular apophyses (three from each wing).

_Dimensions._--Length of the spines 0.3, breadth in the middle 0.03.

_Habitat._--North Pacific, Station 244, surface.

3. _Pristacantha polyodon_, n. sp. (Pl. 130, fig. 7).

Spines in the distal half four-sided prismatic, thin, with pyramidal apex;

in the basal half much broader, four-winged, with a large leaf-cross on the

base. From the four wings of the basal half arises a variable number of

slender teeth or triangular apophyses, commonly sixteen to twenty-four,

often irregular (four to six from each wing).

_Dimensions._--Length of the spines 0.3 to 0.4, breadth in the distal part

0.007 to 0.01, in the basal part 0.02 to 0.03.

_Habitat._--South Pacific (off New Zealand), Station 169, surface.

Family XXXVII. #QUADRILONCHIDA#, Haeckel (Pl. 131).

_Acanthostaurida_, Haeckel, 1881, Prodromus, p. 466.

_Definition._--ACANTHARIA with twenty radial spines of very unequal size,

disposed according to the law of the Icosacantha; four equatorial spines

much larger than the sixteen others. No lattice-shell.

The family #Quadrilonchida# differs from the foregoing ancestral family,

the Astrolonchida, in the unequal development of the twenty radial spines.

The four equatorial spines are constantly much larger, and often also of

another form and shape, than the sixteen other spines; often also among

these the eight tropical spines are larger and of another form than the

eight polar spines. Therefore the five parallel girdles or zones of every

four spines, which in the Astrolonchida are equal, are here distinctly

unequal. The whole body is flattened and compressed in the direction of the

spineless axis, so that the equatorial plane is larger than any other

plane, laid through the centre. In consequence of this flattening the

central capsule is also commonly compressed and flattened, lenticular or

discoidal, rarely spherical. In the Astrolonchida the "promorph" or the

"geometrical fundamental form" is constantly a square double pyramid, the

axes of which are of equal length. In the Quadrilonchida it becomes a

square double pyramid, the two equatorial axes of which (or the diagonals

of the square) are constantly longer than all other axes.

In the simpler forms of Quadrilonchida are found only two different kinds

of spines, the four larger equatorial spines being of the same size and

form, and the sixteen smaller {767}spines also not differing from one

another (_Acanthostaurus_, &c.). But in the majority of this family there

are three different kinds: four larger equatorial spines, eight tropical

spines of middle size, and eight smaller polar spines (_Belonostaurus_,

&c.); the latter become sometimes rudimentary, so that only twelve spines

are developed (four larger equatorial and eight smaller tropical spines).

In this case the development of the flat discoidal body is much stronger in

the equatorial plane than in all other planes. These discoidal or

lenticular Quadrilonchida exhibit a relation to the spherical Astrolonchida

similar to that which the #Discoidea# exhibit to the #Sphæroidea# among the

#Sphærellaria#.

Report on the Radiolaria Collected by H.M.S. Challenger During the Years 1873-1876, First Part: Porulosa (Spumellaria and Acantharia) Report on the Scientific Results of the Voyage of H.M.S. Challenger During the Years 1873-76, Vol. XVIII · 第 24 / 27 章

Opposed to the Icosacantha, under the name "Adelacantha," is the small