Chapter XI: Literature and History (23)

All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the rings; the fourth ring twice as broad as the first. Pores regular, circular; in the inner rings one pore on the breadth, in the outer rings two to three pores. Radial beams piercing, numerous, prominent on the margin.

_Dimensions._--Diameter of the disk (with four rings) 0.1; breadth of the inner rings 0.006, of the outer 0.012; pores 0.0015.

_Habitat._--Fossil in the rocks of Barbados; living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.

18. _Porodiscus duplex_, Haeckel.

_Discospira duplex_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf.
vi. fig. 4.

All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the broad rings. Pores regular, circular; in the inner rings two to three, in the outer four to five on the breadth. Radial beams interrupted. Margin of the rings thorny.

_Dimensions._--Diameter of the disk (with three rings) 0.15; breadth of the rings 0.02 to 0.04; pores 0.007.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

19. _Porodiscus semispiralis_, n. sp. (Pl. 41, fig. 4).

All rings of the disk spirally convoluted, divided by four radial, perpendicularly crossed and zigzag shaped beams into four quadrants; the quarter rings of each quadrant halving the rings of each adjacent quarter. Half spiral line often irregular or partly interrupted. Breadth of all rings nearly equal. Pores irregular, roundish, two on the breadth of each ring. Margin of the disk dentated.

_Dimensions._--Diameter of the disk (with nine rings) 0.22; breadth of each ring 0.012; pores 0.002 to 0.006.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 5. _Atactodiscus_, Haeckel, 1881, Prodromus, p. 459.

_Definition._--Rings of the disk more or less irregular, partly concentric, partly spirally convoluted, often interrupted.

{498}20. _Porodiscus deformis_, Haeckel.

_Discospira deformis_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf.
vi. fig. 6.

Rings of the disk irregular, partly concentric, partly spiral, often interrupted, increasing in breadth from the centre. Radial beams not piercing; pores regular, circular, two to six on the breadth of the different rings. (Very variable and irregular, sometimes more spiral, at other times more concentric, but always with equal pores.)

_Dimensions._--Diameter of the disk (with four rings) 0.18; breadth of the first ring 0.014, of the second 0.03, of the fourth 0.06; pores 0.005.

_Habitat._--Fossil in the Tertiary rocks of Barbados and Sicily; living in the Central Pacific, Stations 266 to 268, depths 2700 to 2900 fathoms.

21. _Porodiscus irregularis_, n. sp. (Pl. 41, fig. 7).

_Atactodiscus irregularis_, Haeckel, 1881, Prodromus, p. 459.

_Perispongidium irregulare_, Haeckel, 1878, MS. et Atlas (pl. xli. fig.
7).

Rings of the disk irregular, partly concentric, partly spiral, often interrupted, with nearly equal breadth. Radial beams not piercing; pores irregular, roundish, two to four on the breadth of each ring; network in the periphery of the disk spongy. (Very variable and irregular, sometimes more spiral, at other times more concentric; disk in the peripheral part often more or less spongy. Differs from the preceding by the equal breadth of the rings and the different size of the pores.)

_Dimensions._--Diameter of the disk (with six rings) 0.15; breadth of each ring 0.011; pores 0.002 to 0.004.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in Barbados.

Genus 215. _Perichlamydium_,[254] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Porodiscida# with a simple circular disk (without radial spines and chambered arms), surrounded on the margin by a thin porous (but not chambered) equatorial girdle.

The genus _Perichlamydium_ differs from _Porodiscus_ only in the development of a thin, porous, equatorial girdle, which surrounds the circular margin of the chambered disk. This girdle lies in the equatorial plane of the lenticular disk, and represents a very delicate siliceous plate, perforated by numerous small pores. Sometimes the proximal part of the girdle is ribbed by thin radial beams, the distal prolongations of the radial rods of the central disk. If these ribs reach the margin of the girdle and are prominent over it, _Perichlamydium_ passes over into _Stylochlamydium_.

{499}1. _Perichlamydium praetextum_, Ehrenberg.

_Perichlamydium praetextum_, Ehrenberg, 1847, Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 21 (non
20).

_Perichlamydium praetextum_, Haeckel, 1862, Monogr. d. Radiol., p. 495.

All rings of the disk (three to four) concentric, circular, of equal breadth, with interrupted (not piercing) radial beams. Equatorial girdle without radial beams, nearly as broad as the disk; its circular pores of the same size as those of the disk; about two pores on the breadth of each ring.

_Dimensions._--Diameter of the disk (without the girdle, with four rings) 0.11; breadth of each ring 0.012; breadth of the girdle 0.06 to 0.1; pores 0.004.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, surface; also fossil in the Tertiary rocks of Barbados and Sicily.

2. _Perichlamydium saturnus_, n. sp. (Pl. 41, fig. 5).

All rings of the disk (three to four) concentric, circular (sometimes partly concentric, circular, partly spiral, or irregular), with interrupted (not piercing) radial beams. Equatorial girdle without radial beams, about half as broad as the disk; its circular pores very small, scarcely half as large as those of the disk; about three pores on the breadth of each ring. (Very variable in the ring-form, differs from the preceding in the small pores of the girdle.)

_Dimensions._--Diameter of the disk (without the girdle, with three rings) 0.11; breadth of each ring 0.02, pores 0.004, breadth of the girdle 0.05, pores 0.002.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

3. _Perichlamydium accrescens_, Haeckel.

_Discospira accrescens_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114,
Taf. vi. fig. 5.

All rings of the disk (six to seven) not concentric, convoluted in a simple spiral, of nearly equal breadth, with interrupted (not piercing) radial beams. Equatorial girdle in the proximal part with numerous radial beams, which do not reach its margin; its pores half as large as those of the disk, where one to two pores arise on the breadth of each ring. (The girdle becomes twice to three times as broad as in the figure of Stöhr.)

_Dimensions._--Diameter of the disk (with seven rings, without the girdle) 0.13; breadth of each ring 0.007 to 0.01; pores 0.0036; breadth of the girdle 0.05, pores of it 0.0017.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel); living in the Central Pacific, Station 266, depth 2750 fathoms.

4. _Perichlamydium spirale_, Ehrenberg.

_Perichlamydium spirale_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 80, Taf. xxii. fig. 12.

All rings of the disk (three to four) not concentric, convoluted in a simple spiral, of increasing breadth from the centre; connected by numerous piercing radial beams. Equatorial girdle about {500}half as broad as the disk, without radial beams; its pores of the same size as those of the disk, regular, circular; three pores on the breadth of the first ring, six pores of the fourth ring.

_Dimensions._--Diameter of the disk (with four rings, without the girdle) 0.12; breadth of the first ring 0.01, of the fourth 0.02; breadth of the girdle 0.05; pores 0.003.

_Habitat._--Fossil in the rocks of Barbados.

Subfamily 3. OMMATODISCIDA, Stöhr, 1880, Palæontographica, vol. xxvi. p. 115.

_Definition._--#Porodiscida# without radial appendages of the concentrically annulated disk, but distinguished by one single or two opposite large marginal oscula, or wide openings on the margin of the disk, armed with a coronet of spines.

Genus 216. _Ommatodiscus_,[255] Stöhr, 1880, Palæontographica, vol. xxvi. p. 115.

_Definition._--Porodiscida without chambered arms and radial spines on the margin of the circular or elliptical disk, but with one large marginal osculum or opening surrounded by a coronet of spines.

The genus _Ommatodiscus_, together with the following _Stomatodiscus_, form the peculiar small subfamily of Ommatodiscida, founded by Stöhr in 1880 (_loc. cit._). These remarkable Porodiscida, very nearly allied to _Porodiscus_, are distinguished by one or two large openings on the margin of the disk, and these "marginal oscula" are constantly armed with a coronet of spines (comparable to the osculum coronatum of _Sycon_ in the Calcispongiæ). Probably in the living Ommatodiscida the osculum is the door from which a "sarcode-flagellum" issues (comp. above, p. 407). Perhaps this osculum is comparable to the peculiar coronet of spines which is developed on one pole of the shell axis in some Ellipsida (_Lithomespilus_, _Lithapium_). The internal structure of the disk is commonly more or less obscure, as the lenticular disk is much thickened, sometimes nearly ellipsoidal. It is possible that the Ommatodiscida are more nearly related to the Lithelida than to the Porodiscida; but there is no indication of an internal trizonal medullary shell. Also the apparent resemblance to the Cyrtida is of no morphological value; both groups are of quite independent phylogenetic origin.

Subgenus 1. _Ommatodiscinus_, Haeckel.

_Definition._--Disk circular.

1. _Ommatodiscus decipiens_, Stöhr.

_Ommatodiscus decipiens_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 115,
Taf. vi. figs. 8, 8_a._

Disk circular, with two chambered rings around the spherical central chamber, of equal breadth. Chambers twice as high as broad. Pores very small, one-third as broad as the bars {501}between them, two on the breadth of each ring. Osculum of the same breadth as the central chamber, surrounded by numerous very short teeth.

_Dimensions._--Diameter of the disk 0.12; breadth of the central chamber and of each ring 0.03; pores 0.0015.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

2. _Ommatodiscus stöhrii_, n. sp.

Disk circular with three chambered rings around the spherical central chamber, of equal breadth. Chambers broader than high. Pores of the same breadth as the bars between them, four on the breadth of each ring. Osculum of the same breadth as the central chamber, surrounded by a corona of ten to twenty thin, bristle-shaped teeth, as long as its diameter.

_Dimensions._--Diameter of the disk 0.2; breadth of the central chamber and of each ring 0.03; pores 0.004.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

3. _Ommatodiscus circularis_, n. sp.

Disk circular, with four circular chambered rings around the spherical central chamber, of increasing breadth; the fourth ring twice as broad as the second. Chambers about as broad as high. Pores large, twice as broad as the bars, one to two on the breadth of each ring. Osculum twice as broad as the central chamber, surrounded by a coronal of strong conical teeth, twice as long as its diameter.

_Dimensions._--Diameter of the disk 0.18; breadth of the central chamber and inner rings 0.015, of the outer rings 0.03; pores 0.01.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. _Ommatodisculus_, Haeckel.

_Definition._--Disk elliptical.

4. _Ommatodiscus haeckelii_, Stöhr.

_Ommatodiscus haeckelii_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 115,
Taf. vi. figs. 7, 7_a._

Disk elliptical (6 : 7), with four chambered rings around the elliptical central chamber, of equal breadth. Chambers about as high as broad. Pores small, half as broad as the bars, two on the breadth of each ring. Osculum three times as broad as the central chamber, surrounded by a crown of strong conical teeth.

_Dimensions._--Length of the disk 0.18, breadth 0.16; breadth of each ring and of the central chamber 0.02; pores 0.003.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel).

{502}5. _Ommatodiscus lævigatus_, Stöhr.

_Ommatodiscus lævigatus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 116,
Taf. vi. figs. 9, 9_a._

Disk elliptical (3 : 4), with three chambered rings around the circular central chamber, the third ring half as broad as the second. Chambers twice as high as broad. Pores very small, one-third as broad as the bars. Osculum twice as broad as the central chamber, armed with a crown of short conical teeth.

_Dimensions._--Length of the disk 0.15, breadth 0.11; breadth of inner rings 0.02, of the outer 0.01; pores 0.0017.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

6. _Ommatodiscus fragilis_, Stöhr.

_Ommatodiscus fragilis_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 116,
Taf. vi. figs. 10, 10_a._

Disk elliptical (4 : 5), with five chambered rings around the elliptical central chamber, the fifth ring twice as broad as each of the others. Chambers about as high as broad. Pores very small, one-fifth as broad as the bars. Osculum three times as broad as the central chamber, surrounded by a coronet of short teeth.

_Dimensions._--Length of the disk 0.17, breadth 0.13; breadth of the inner rings 0.01, of the outer 0.02; pores 0.001.

_Habitat._--Fossil in Tertiary rocks of Sicily and Barbados; living in depths of the Tropical Atlantic and Pacific, Station 353, depth 2965 fathoms, Station 265, depth 2900 fathoms, &c.

Genus 217. _Stomatodiscus_,[256] n. gen.

_Definition._--#Porodiscida# without chambered arms and radial spines on the margin of the circular or elliptical disk, but with two large, opposite, marginal oscula, or openings surrounded by a coronet of spines.

The genus _Stomatodiscus_ has the same characteristic structure as the foregoing _Ommatodiscus_, and differs from it only in the duplication of the large marginal openings. Whilst in the latter there is only one such marginal osculum, here we find on the margin of the disk two oscula, opposite on the poles of one equatorial axis.

1. _Stomatodiscus amphistomus_, n. sp.

Disk circular, with three concentric rings of equal breadth around the central chamber. Pores irregular, roundish, about two on the breadth of each ring. Surface of the lenticular shell spiny. On two opposite points of the margin a large osculum, three to four times as broad as the central chamber, armed with a coronet of strong pyramidal spines of different length, the longest equal to the radius of the disk.

{503}_Dimensions._--Diameter of the disk (with three rings) 0.12; breadth of each ring 0.016; pores 0.004.

_Habitat._--South Pacific, Station 302, depth 1450 fathoms.

2. _Stomatodiscus osculatus_, n. sp. (Pl. 48, fig. 8).

Disk elliptical, nearly twice as long as broad, with three concentric rings around the elliptical central chamber, one piercing radial beam in the main axis, the other beams interrupted. Surface of the shell with small scattered thorns. Pores very irregular, roundish, partly aggregated in groups of four to eight smaller porules. On both poles of the main axis a large elliptical marginal osculum, about as large as the central chamber, armed with a coronet of short conical spines.

_Dimensions._--Length of the disk (with three rings) 0.18, breadth 0.1; pores 0.001 to 0.006.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subfamily 4. STYLODICTYIDA, Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Porodiscida# with solid radial spines on the margin of the concentrically annulated disk, situated in the equatorial plane of the disk (without chambered arms and marginal oscula).

Genus 218. _Xiphodictya_,[257] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with two opposite, solid, radial spines on the margin of the circular or elliptical disk.

The genus _Xiphodictya_ opens the series of the Stylodictyida or of those Porodiscida in which the margin of the chambered disk is armed with solid radial spines, all situated in the equatorial plane of the disk. _Xiphodictya_ exhibits the minimum number of spines, two being opposite on the poles of one equatorial axis of the disk. It repeats, therefore, in this family the same amphistylic formation as _Sethostylus_ in the Phacodiscida and _Stylocyclia_ in the Coccodiscida.

Subgenus 1. _Xiphodictyon_, Haeckel.

_Definition._--All rings of the disk concentric, circular.

1. _Xiphodictya amphibelonia_, n. sp. (Pl. 42, fig. 10).

All rings of the disk concentric, circular, of equal breadth. Pores irregular, roundish, one and a half to two on the breadth of each ring. Margin of the disk thorny, of the same thickness as {504}the central part of the medal-shaped or cylindrical disk. Two opposite radial spines very long and thin, cylindrical, twice to three times as long as the diameter of the disk, only half as thick as the breadth of one ring.

_Dimensions._--Diameter of the disk (with five rings) 0.17; breadth of each ring 0.014; pores 0.003 to 0.012.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

2. _Xiphodictya amphirrhopalia_, n. sp. (Pl. 42, fig. 11).

All rings of the disk concentric, circular, with increasing breadth from the centre; the fifth ring twice as broad as the second. Central chamber very large. Margin of the lenticular disk thorny, much thinner than the central part. Pores irregular, roundish, two to three on the breadth of each ring. Two opposite radial spines club-shaped, about as long as the diameter of the disk, in the outer spindle-shaped part three to four times as broad as at the base.

_Dimensions._--Diameter of the disk (with six rings) 0.17; breadth of the second ring 0.008, of the fifth ring 0.016.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms; also fossil in the Tertiary rocks of Sicily (Caltanisetta).

Subgenus 2. _Xiphospira_, Haeckel.

_Definition._--All rings of the disk or a part of them not concentric, spirally convoluted; sometimes irregular or interrupted.

3. _Xiphodictya staurospira_, n. sp. (Pl. 42, fig. 12).

All rings of the disk not concentric, half spiral. Four radial beams, crossed perpendicularly and zigzag-shaped, divide each ring into four quadrants; the quarter-ring of each quadrant halves the two adjacent rings. All rings of equal breadth. Pores irregular, roundish, two on the breadth of each ring. Two opposite radial spines pyramidal, somewhat shorter than the diameter of the disk.

_Dimensions._--Diameter of the disk (with six rings) 0.16; breadth of each ring: 0.014; pores 0.003 to 0.007.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

4. _Xiphodictya heliospira_, n. sp.

All rings of the disk not concentric, convoluted in a simple, regular, spiral line; all nearly of equal breadth. Pores subregular, circular, two on the breadth of each ring. Two opposite radial spines conical, about as long as the radius of the disk. Margin of the disk thorny. (Differs from _Stylodictya heliospira_, Pl. 41, fig. 8, mainly by the two strong, opposite, radial spines.)

{505}_Dimensions._--Diameter of the disk (with six rings) 0.14; breadth of each ring 0.01 to 0.012; pores 0.002 to 0.006.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

Genus 219. _Tripodictya_,[258] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with three solid, equidistant, radial spines on the margin of the circular or triangular disk.

The genus _Tripodictya_ exhibits three radial spines on the margin of the disk, divergent at equal angles; rarely in some specimens the angles differ more or less. Perhaps this genus bears a near relation to the Dictyastrida (or to the Euchitonida with three chambered arms--_Dictyastrum_, _Euchitonia_, &c.).

1. _Tripodictya trigonaria_, n. sp. (Pl. 42, fig. 8).

All rings of the disk concentric, triangular, with three equal convex sides, all of the same breadth; first and second rings with three simple chambers, third and fourth rings with six chambers, fifth ring with twelve chambers. Central chamber also equilateral triangular, from its three corners arise three piercing perradial beams; from the second ring arise three interradial beams, alternate with the latter; from the fourth ring between these and the former arise six adradial beams. Pores subregular, two on the breadth of each ring. Three marginal spines pyramidal, as long as the radius of the disk and as broad as one ring.

_Dimensions._--Diameter of the disk (with five rings) 0.11; breadth of each ring 0.011; pores 0.004.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

2. _Tripodictya triacantha_, n. sp. (Pl. 42, fig. 7).

All rings of the disk concentric, circular, of the some breadth, connected by very numerous irregular radial beams, the number of which increases towards the periphery. Pores irregular, roundish, two on the breadth of each ring. Three marginal spines spindle-shaped, as long as the radius of the disk, and in the middle part as broad as one ring.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.012; pores 0.004.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

3. _Tripodictya tribelonia_, n. sp. (Pl. 42, fig. 9).

All rings of the disk, or a part of them, not concentric, spirally convoluted, of equal breadth, connected by numerous irregular, interrupted radial beams, the number of which increases from the centre. (In one marginal view of the disk, Pl. 42, fig. 9, the disk seemed to be composed of seven {506}parallel chambered plates in the central part, and five similar plates in the peripheral part.) Pores irregular, roundish, three on the breadth of each ring. Three marginal spines long and thin, cylindrical (as in _Staurodictya cruciata_, Pl. 42, fig, 4), longer than the diameter of the disk, and half as thick as one ring.

_Dimensions._--Diameter of the disk (with nine rings) 0.18; breadth of each ring 0.01; pores 0.002 to 0.004.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

Genus 220. _Staurodictya_,[259] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with four solid radial spines (commonly crossed at right angles) on the margin of the circular or quadrangular disk.

The genus _Staurodictya_ is characterised by four marginal spines, lying opposite in pairs in two crossed equatorial diameters of the disk, perpendicular one to another. Sometimes the regular rectangular position of the spines becomes more or less irregular. Commonly the marginal spines are the extreme prolongations of four internal crossed radial beams, which are either rectilinear or zigzag-shaped. In the latter case the concentric disposition of the circular rings becomes more or less spiral. Perhaps _Staurodictya_ has a near relation to the Stauralastrida (or to the Euchitonida with four crossed chambered arms--_Stauralastrum_, _Histiastrum_, &c.).

Subgenus 1. _Staurodictyon_, Haeckel.

_Definition._--All rings of the disk concentric (commonly circular, sometimes with four incisions, produced by two crossed constrictions, or nearly square).

1. _Staurodictya medusa_, n. sp. (Pl. 42, fig. 3).

All rings of the disk concentric, of nearly equal breadth, divided into four quadrants by two perradial constrictions (perpendicular one to another). Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines strong, pyramidal, nearly as long as the radius of the disk. Margin between them denticulated.

_Dimensions._--Diameter of the disk (with four rings) 0.13; breadth of each ring 0.015; pores 0.002 to 0.01.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

2. _Staurodictya ciliata_, n. sp. (Pl. 42, fig. 2).

All rings of the disk concentric, of nearly equal breadth, circular or roundish, without perradial constrictions. Pores subregular, circular, three to four on the breadth of each ring. Four marginal {507}spines short, pyramidal, about as long as the breadth of one ring. Margin between them ciliated, with thin radial bristles.

_Dimensions._--Diameter of the disk (with four rings) 0.13; breadth of each ring 0.015; pores 0.0025.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

3. _Staurodictya elegans_, n. sp. (Pl. 42, fig. 1).

All rings of the disk concentric, circular, or roundish, of increasing breadth towards the margin; the fifth ring twice as broad as the first. Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines very large, conical, with a thin pedicle at the base, cancellated by ten to twelve deep furrows, about as long as the radius of the disk and three times as long as broad at the base (above the pedicle). Margin between them ciliated, with numerous short radial spines.

_Dimensions._--Diameter of the disk (with six rings) 0.14; breadth of the inner rings 0.006, of the outer 0.012; pores 0.002 to 0.008.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

4. _Staurodictya quadrispina_, Haeckel.

_Stylodictya quadrispina_, Haeckel, 1862, Monogr. d. Radiol., p. 496,
Taf. xxix. fig. 4.

All rings of the disk concentric, circular, of increasing breadth towards the margin; the fourth ring twice as broad as the second. Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines short and thin, conical, about as long as the breadth of one ring. Margin between them smooth.

_Dimensions._--Diameter of the disk (with six rings) 0.12; breadth of the inner rings 0.006, of the outer rings 0.012; pores 0.001 to 0.006.

_Habitat._--Mediterranean, Atlantic (Canary Islands), surface.

Subgenus 2. _Staurospira_, Haeckel.

_Definition._--All rings of the disk or a part of them not concentric, spirally convoluted; spiral line simple or double, sometimes half or irregular, interrupted.

5. _Staurodictya cruciata_, n. sp. (Pl. 42, figs. 4, 5).

All rings of the disk nearly of the same breadth, not concentric, half-spiral, interrupted by four zigzag-shaped radial beams crossed in two diameters perpendicular one to another. The quarter ring of each quadrant halving both neighbouring quarters. Pores irregular, roundish, two on the breadth of each ring. Pores of the outermost (eighth) ring much smaller than the others. Four marginal spines cylindrical or nearly spindle-shaped, thick, about as long as the radius of the disk. Margin between them smooth.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.011; pores 0.004.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

{508}6. _Staurodictya splendens_, Haeckel.

_Stylodictya splendens_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 84, Taf. xxiii. fig. 9.

All rings of the disk nearly of the same breadth, not concentric, half-spiral, interrupted by four zigzag-shaped perradial beams, crossed in two diameters. The quarter ring of each quadrant halving both neighbouring quarters. Pores regular, circular, only one single on the breadth of each ring. Four marginal spines conical or spear-shaped, about half as long as the radius of the disk. Margin between them ciliated, with short bristle-shaped radial spines.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.012; pores 0.004.

_Habitat._--Fossil in the rocks of Barbados.

7. _Staurodictya grandis_, n. sp.

All rings of the disk (twelve to sixteen) of the same breadth, not concentric, irregular, partly spiral, interrupted by irregular turnings, and by ramified radial beams, which divide each ring into numerous square chambers. Pores subregular, circular, only one single on the breadth of each ring (and on each chamber). Four marginal spines short and stout, conical, twice as long as broad at the base, four to five times as long as the breadth of one ring. Margin between them dentated.

_Dimensions._--Diameter of the disk (with sixteen rings) 0.3; breadth of each ring 0.01; pores 0.005.

_Habitat._--Pacific, central area, Stations 265 to 268, depth 2900 fathoms; also fossil in the Tertiary rocks of Barbados.

8. _Staurodictya ocellata_, Haeckel.

_Stylodictya ocellata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 84, Taf. xxiii. fig. 7.

All rings of the disk irregular, not concentric, half-spiral, interrupted by four zigzag-shaped, crossed, radial beams; the quarter ring of each quadrant halving both neighbouring quarters. Breadth of the rings increasing towards the periphery; the fourth ring twice as broad as the second. Pores irregular, with increasing size from the centre, three on the breadth of each ring. Four marginal spines thick and long, cylindrical; margin between them smooth.

_Dimensions._--Diameter of the disk (with four rings) 0.1; breadth of the inner rings 0.01, of the outer 0.02; pores 0.002 to 0.006.

_Habitat._--Fossil in the rocks of Barbados.

_Stylodictya haeckelii_, Zittel, 1876, L. N. 29, p. 85, Taf. ii. fig. 9, is a fossil Cretaceous species, related to _Stylodictya multispina_.

{509}Genus 221. _Stylodictya_,[260] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Porodiscida# with numerous (five or more, commonly eight to twelve) solid radial spines, regularly or irregularly disposed on the margin of the circular or polygonal disk; margin simple, without a porous equatorial girdle.

The genus _Stylodictya_ comprises the majority of this subfamily, in which the number of the marginal spines exceeds four. Commonly we find eight to twelve spines, more or less regularly disposed (four perradial and four interradial, or four perradial and eight adradial); but often also the number and disposition become irregular (sometimes very large). In my Monograph (1862 pp. 495, 515) I had separated the concentric disks with closed circular rings (as true _Stylodictya_, s. str.) from the spiral disks with convoluted rings (_Stylospira_). But I retain these two groups here only as two subgenera, as intermediate forms between them are very common, and often a part of the disk concentric, a part spiral (compare above, p. 492).

Subgenus 1. _Stylodictyon_, Haeckel, 1862, Monogr. d. Radiol., p. 495.

_Definition._--All rings of the disk concentric, commonly circular (rarely a little elliptical or polygonal).

1. _Stylodictya gracilis_, Ehrenberg.

_Stylodictya gracilis_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 28.

_Stylodictya gracilis_, Ehrenberg, 1873, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 257; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf.
xxiii. fig. 3.

_Stylodictya gracilis_, Haeckel, 1862, Monogr. d. Radiol., p. 499.

All rings of the disk concentric, circular, of equal breadth (the first ring sometimes, but not constantly, four-lobed). Pores regular, circular, small, three on the breadth of each ring. Four perradial beams (crossed in two perpendicular diameters) beginning from the circular central chamber, four interradial beams from the first or second ring (sometimes others between them). Beams prolonged into eight to twelve (or more) marginal spines, bristle-shaped, as long as the radius of the shell.

_Dimensions._--Diameter of the disk (with four rings) 0.12; breadth of each ring 0.013; pores 0.0025.

_Habitat._--Fossil in Tertiary rocks of Barbados and Nicobar; living in the depths of the Pacific and Atlantic.

{510}2. _Stylodictya multispina_, Haeckel.

_Stylodictya multispina_, Haeckel, 1862, Monogr. d. Radiol., p. 496, Taf.
xxix. fig. 5.

_Stylodictya forbesii_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 160, Taf. xxiii. fig. 6.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, two and a half to three on the breadth of each ring. Eight to twelve radial beams beginning from the central chamber, others from the inner rings. Commonly from the third or fourth ring arise twenty-four to thirty (sometimes forty or more) piercing beams, which are prolonged at the margin into bristle-shaped radial spines, as long as the breadth of two to four rings.

_Dimensions._--Diameter of the disk (with seven rings) 0.2; breadth of each ring 0.013; pores 0.004.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface and various depths.

3. _Stylodictya hastata_, Ehrenberg.

_Stylodictya hastata_, Ehrenberg, 1873, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin, p. 257; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf.
xxiii. fig. 5.

_Stylodictya gracilis_, Bury, 1862, Polycystins of Barbados, pl. ii. fig.
1.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, very small, two on the breadth of each ring. Eight to twelve marginal spines very large, spear-shaped, sulcated, pyramidal, nearly as long as the diameter of the disk, with a thin pedicle at the base, above this as thick as the breadth of one ring.

_Dimensions._--Diameter of the disk (with five rings) 0.13; breadth of each ring 0.012; pores 0.003.

_Habitat._--Fossil in the rocks of Barbados.

4. _Stylodictya stellata_, Bailey.

_Stylodictya stellata_, Bailey, 1856, Amer. Journ., vol. xxii. p. 6, pl.
i. fig. 20.

_Stylodictya stellata_, Haeckel, 1862, Monogr. d. Radiol., p. 499.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, very small, two on the breadth of each ring. Marginal spines fourteen (probably variable in number, twelve to sixteen), very thick and short, conical; their length seems to be equal to their basal breadth and to the breadth of one ring. Related to _Stylochlamydium_?

_Dimensions._--Diameter of the disk (with five rings) 0.11; breadth of each ring 0.01; pores 0.003.

_Habitat._--North Pacific, depths of the Kamtschatka Sea, Bailey; Station 241, depth 2300 fathoms.

5. _Stylodictya arachnia_, Haeckel.

_Stylodictya arachnia_, Haeckel, 1862, Monogr. d. Radiol., p. 497.

_Stylocyclia arachnia_, J. Müller, 1856, p. 492; Abhandl. d. k. Akad. d.
Wiss. Berlin, 1858, p. 41, Taf. i. figs. 8, 9.

All rings of the disk concentric, circular, or polygonal; their breadth increases from the centre towards the periphery, so that the fourth or fifth ring is twice as broad as the second. Pores {511}subregular, circular, two on the breadth of each ring. Radial beams partly piercing. Marginal spines eight to sixteen (commonly twelve), bristle-shaped, very thin, once to three times as long as the diameter of the disk. (On the numerous varieties of this common species compare my Monograph, 1862, p. 498.)

_Dimensions._--Diameter of the disk (with ten rings) 0.22; breadth of the inner rings 0.004 to 0.008, of the outer 0.012 to 0.015; pores 0.003 to 0.005.

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

6. _Stylodictya solmaris_, n. sp.

All rings of the disk concentric, polygonal, with eight to sixteen rounded corners; their breadth increases from the centre; eighth ring twice as broad as the second. Pores subregular circular, large, only one pore on the breadth of each ring. Twenty to thirty marginal spines, bristle-shaped, undulating, about as long as (or longer than) the diameter of the disk.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of the inner rings 0.005, of the outer 0.012; pores 0.004 to 0.008.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

7. _Stylodictya octogonia_, n. sp.

All rings of the disk concentric, increasing in breadth from the centre. The outer rings (five to eight) regular, octogonal, twice as broad as the circular inner rings. Pores subregular, circular, two to three on the breadth of each ring. Eight piercing perradial spines (alternating with the eight corners of the octogonal rings) bristle-shaped, longer than the diameter of the disk.

_Dimensions._--Diameter of the disk (with eight rings) 0.24; breadth of the inner rings 0.006, of the outer 0.014; pores 0.005 to 0.01.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

Subgenus 2. _Stylodictula_, Haeckel.

_Definition._--Rings of the disk partly concentric, completely annular; partly spiral or interrupted, often irregular.

8. _Stylodictya perispira_, n. sp.

Inner rings of the disk (two to four) concentric, circular, or roundish, outer rings forming a simple spiral, breadth a little increasing from the centre. Pores subregular, circular, about two on the breadth of each ring. Marginal spines bristle-shaped, ten to fifteen, about as long as the diameter of the disk.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.013; pores 0.004.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

{512}9. _Stylodictya centrospira_, n. sp. (Pl. 41, fig. 9).

Inner rings of the disk (three or four) convoluted in a simple or double spiral, often interrupted or irregular; outer rings (two to three) concentric, circular, or roundish. Breadth of the rings variable, irregular. Pores irregular, of very different sizes, in the outer concentric part twice to four times as large as in the inner spiral part. Radial beams partly interrupted, partly piercing. Marginal spines fifty to eighty, very variable in size and number, commonly fifteen to twenty strong conical spines, twice to three times as long as the ring-breadth, and numerous (thirty to sixty) smaller spines. Very variable.

_Dimensions._--Diameter of the disk (with seven rings) 0.2; breadth of the rings 0.01 to 0.02; pores 0.002 to 0.01.

_Habitat._--Pacific, central area, Stations 263 to 274, depth 2350 to 2925 fathoms.

10. _Stylodictya setigera_, Ehrenberg.

_Stylodictya setigera_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 84, Taf. xxiii. fig. 4.

Inner rings of the disk (two to three) convoluted in a simple or double spiral, outer rings (two to three) concentric, circular, or roundish. Breadth of the rings nearly equal. Pores regular, circular, three on the breadth of each ring. Marginal spines twenty to forty, bristle-shaped, about twice as long as the ring-breadth. (The specimen figured by Ehrenberg was a young one; in older specimens I found the inner spiral disk surrounded by two to three concentric circular rings.)

_Dimensions._--Diameter of the disk (with six rings) 0.16; breadth of the rings 0.12; pores 0.003.

_Habitat._--Fossil in the rocks of Barbados; also living in the depths of the Central Pacific, Station 266, depth 2750 fathoms.

Subgenus 3. _Stylospira_, Haeckel, 1862, Monogr. d. Radiol., p. 515.

_Definition._--All rings of the disk convoluted in a simple or double spiral (sometimes also in quartered half-spirals).

11. _Stylodictya heliospira_, n. sp. (Pl. 41, fig. 8).

_Stylospira heliospira_, Haeckel, 1879, MS.

All rings of the disk convoluted in a simple regular spiral, increasing in breadth from the centre towards the periphery; the sixth ring twice as broad as the second. Pores irregular, roundish, two on the breadth of each ring. Marginal spines numerous, thirty to forty, bristle-shaped, nearly half as long as the radius of the disk.

_Dimensions._--Diameter of the disk (with seven rings) 0.16; breadth of the inner rings 0.008, of the outer 0.016; pores 0.002 to 0.006.

_Habitat._--Mediterranean, Portofino near Genoa, surface; also fossil in the Tertiary rocks of Sicily; Caltanisetta, Haeckel.

{513}12. _Stylodictya hertwigii_, Haeckel.

_Stylospira arachnia_, R. Hertwig, 1879, Organismus d. Radiol., p. 59,
Taf. vi. fig. 8.

All rings of the disk convoluted in a simple regular spiral, with increasing breadth from the centre; the fifth ring twice as broad as the second. Pores regular, circular, two on the breadth of each ring. Twelve piercing radial beams and some others interrupted, prolonged into twelve to twenty radial marginal spines, bristle-shaped, about as long as the diameter of the disk.

_Dimensions._--Diameter of the disk (with five rings) 0.15; breadth of the second ring 0.01, of the fifth 0.02; pores 0.006.

_Habitat._--Mediterranean (Messina), R. Hertwig.

13. _Stylodictya dujardinii_, Haeckel.

_Stylospira dujardinii_, Haeckel, 1862, Monogr. d. Radiol., p. 515, Taf.
xxix. figs. 9, 10.

All rings of the disk convoluted in a simple regular spiral, of nearly equal breadth. Pores regular, circular, two on the breadth of each ring. Very numerous (twenty to thirty or more) piercing radial beams, prolonged into bristle-shaped marginal spines, about as long as the diameter of the disk.

_Dimensions._--Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.004.

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

14. _Stylodictya echinastrum_, Ehrenberg.

_Stylodictya echinastrum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 84, Taf. xxiii. fig. 1.

All rings of the disk convoluted in a double spiral, of nearly equal breadth. Pores irregular, roundish, two to three on the breadth of each ring. Marginal spines numerous, twenty to thirty, of very different size, the largest conical, strong, about as long as the diameter of the disk, and on the base as broad as one ring.

_Dimensions._--Diameter of the disk (with five rings) 0.12; breadth of each ring 0.01; pores 0.002 to 0.006.

_Habitat._--Fossil in the rocks of Barbados.

15. _Stylodictya clavata_, Ehrenberg.

_Stylodictya clavata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 84, Taf. xxiii. fig. 2.

All rings of the disk convoluted in a half spiral, of nearly equal breadth; each ring by four zigzag beams (crossed in two perpendicular diameters) divided into four equal quarters; the spiral line of each quarter ring halving both neighbouring quarters. Pores regular, circular, two on the breadth of each ring. Eight marginal spines short, conical, with thin pedicle; four perradial (as {514}prolongations of the four internal beams) alternating with four interradial spines arising from the margin of the disk.

_Dimensions._--Diameter of the disk (with five rings) 0.13; breadth of each ring 0.014; pores 0.003.

_Habitat._--Fossil in the rocks of Barbados.

Genus 222. _Stylochlamydium_,[261] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with numerous (five or more, commonly eight to twelve) solid radial spines, regularly or irregularly disposed on the margin of the circular or polygonal disk; margin of the disk surrounded by a thin, porous (but not chambered), equatorial girdle.

The genus _Stylochlamydium_ is intermediate between _Perichlamydium_ (with which it was formerly united) and _Stylodictya_. It deals with the former in the peculiar equatorial girdle, with the latter in the radial spines of the disk margin, which pierce the girdle. To both these genera it shows slow transitions, and can hardly be subjected to a sharp definition.

Subgenus 1. _Stylochlamys_, Haeckel.

_Definition._--All rings of the disk concentric, circular (or somewhat polygonal).

1. _Stylochlamydium asteriscus_, n. sp. (Pl. 41, fig. 10).

_Perichlamydium asteriscus_, Haeckel, 1879, MS.

All rings of the disk concentric, circular, or polygonal, with increasing breadth from the centre; the fifth ring twice as broad as the second. Pores irregular, roundish, three to four on the breadth of each ring; in the rings two to six times as large as in the equatorial girdle, which is half as broad or two-thirds as broad as the radius of the disk. Twelve bristle-shaped radial spines are connected by the girdle near to the points; four crossed spines arising from the central chamber; two others between these in each quadrant arising from the first ring.

_Dimensions._--Diameter of the disk (with five rings) 0.15, with the girdle 0.25; breadth of the second ring 0.01, of the fifth ring 0.02; pores 0.001 to 0.005.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Stylochlamydium limbatum_, Haeckel.

_Perichlamydium limbatum_, Ehrenberg, 1847, Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 20.

_Perichlamydium limbatum_, Haeckel, 1862, Monogr. d. Radiol., p. 494.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, two on the breadth of each ring; twice to three times as large as the fine pores of the equatorial girdle, which is {515}about half as broad as the radius of the disk. Twelve (or eleven) bristle-shaped radial spines are connected by the girdle near to the points, irregularly disposed.

_Dimensions._--Diameter of the disk (with five rings) 0.12, with the girdle 0.2, breadth of each ring 0.01; pores 0.001 to 0.003.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Caltanisetta, Grotte.

3. _Stylochlamydium venustum_, Haeckel.

_Perichlamydium venustum_, Bailey, 1856, Amer. Journ., vol. xxii. p. 5,
pl. i. figs. 16, 17.

_Perichlamydium venustum_, Haeckel, 1862, Monogr. d. Radiol., p. 495.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, everywhere of nearly equal size, three on the breadth of each ring, a little smaller in the equatorial girdle, which is about as broad as the radius of the disk. Twenty to twenty-four bristle-shaped radial spines, irregularly disposed, proceed with their free points over the margin.

_Dimensions._--Diameter of the disk (with four rings) 0.1, with the girdle 0.3; breadth of each ring 0.011; pores 0.002.

_Habitat._--North Pacific, Kamtschatka, Bailey.

4. _Stylochlamydium æquale_, Haeckel.

_Perichlamydium æquale_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 109, pl.
v. fig. 2.

All rings of the disk concentric, circular, with increasing breadth from the centre; the sixth ring twice as broad as the second. Pores regular, circular, everywhere of equal size; on the breadth of the inner rings one, of the outer two, of the girdle three pores. Girdle only one-fourth as broad as the radius of the disk. About twenty bristle-shaped radial spines, irregularly disposed, are connected by the girdle near to the points.

_Dimensions._--Diameter of the disk (with six rings) 0.11, with the girdle 0.17; breadth of the second ring 0.006, of the sixth 0.013; pores 0.006.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

Subgenus 2. _Stylochlamyum_, Haeckel.

_Definition._--Rings of the disk all (or in part) not concentric, spirally convoluted or irregular.

5. _Stylochlamydium perispirale_, Haeckel.

_Perichlamydium limbatum_, var. Stöhr, 1880, Palæontogr., vol. xxvi. p.
109, Taf. v. fig. 1.

Inner rings of the disk concentric, circular, outer rings convoluted spirally, all rings of equal breadth. Pores regular, circular, two on the breadth of each ring, twice as large as in the equatorial {516}girdle, which is about half as broad as the radius of the disk. Twelve to sixteen bristle-shaped radial spines, irregularly disposed, are connected by the girdle near to the points.

_Dimensions._--Diameter of the disk (with six rings) 0.12, with the girdle 0.2; breadth of each ring 0.011; pores in the central disk 0.004, in the girdle 0.002.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

6. _Stylochlamydium spongiosum_, Haeckel.

_Perichlamydium spongiosum_, Stöhr, 1880, Palæontogr., vol. xxvi, p. 109,
Taf. v. fig. 3.

Rings of the disk partly concentric, partly spiral, more or less irregular and often interrupted, with increasing breadth from the centre. Central part of the disk more or less spongy and obscure. Equatorial girdle half as broad as the radius of the chambered disk, with smaller pores than the latter, pierced by twenty to thirty thin, bristle-shaped radial beams, which proceed over the margin of the disk.

_Dimensions._--Diameter of the disk (with ten rings) 0.2, with the girdle 0.3; breadth of the rings 0.005 to 0.015; pores 0.001 to 0.005.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms; also fossil in the Tertiary rocks of Barbados and Sicily.

Subfamily 5. EUCHITONIDA, Haeckel.

_Definition._--#Porodiscida# with two or more (commonly three or four) radial chambered or spongy arms on the margin of the concentrically annulated disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 223. _Amphibrachium_,[262] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with two simple, undivided, chambered arms, opposite in one axis, without a patagium.

The genus _Amphibrachium_ opens the long series of the Euchitonida, or of those Porodiscida which bear on the margin of the circular central disk a certain number of chambered arms, composed of a series of chambers which are separated by transverse septa. The first group or tribe of this subfamily is formed by the Amphibrachida, in which the disk bears only two arms opposite on the poles of one axis. The simplest form of these is _Amphibrachium_, in which both arms are simple, equal, and without a patagium or spongy connecticulum.

{517}Subgenus 1. _Amphibrachella_, Haeckel.

_Definition._--Both arms equal, of the same form and size, blunt at the distal end, without a terminal spine.

1. _Amphibrachium sponguroides_, n. sp.

Both opposite arms of the same form and size, nearly cylindrical, three times as long as broad, with six to eight transverse septa or joints, at the distal end rounded, blunt, without a terminal spine.

_Dimensions._--Radius of each arm 0.22, breadth 0.065.

_Habitat._--Antarctic Ocean, Station 154, surface.

2. _Amphibrachium lanceolatum_, n. sp.

Both arms equal, lanceolate, in the middle part three times as broad as at the two ends, two and a half times as long as broad, with eight to nine transverse septa, at the distal end blunt, without a terminal spine.

_Dimensions._--Radius of each arm 0.3, greatest breadth 0.09.

_Habitat._--Pacific, central area, Station 267, depth 2700 fathoms.

3. _Amphibrachium dilatatum_, n. sp. (Pl. 44, fig. 6).

Both arms equal, trapezoidal, somewhat broader than long, on the convex distal end three times as broad as on the narrow base, with five to six transverse septa, without a terminal spine. Central disk large, somewhat irregular, with three to four rings, twice as broad as the base of the arms.

_Dimensions._--Radius of each arm 0.32, basal breadth 0.15, terminal breadth 0.44.

_Habitat._--South Atlantic, off Patagonia, Station 319, surface.

Subgenus 2. _Amphibrachidium_, Haeckel.

_Definition._--Both arms equal, of the same size and form, with terminal spines.

4. _Amphibrachium amphilonche_, n. sp.

Both arms equal, lanceolate, in the middle part four times as broad as at the two ends, twice as long as broad; on the distal end of each arm is a long conical spine.

_Dimensions._--Radius of each arm (without terminal spine) 0.2, breadth 0.08.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{518}5. _Amphibrachium capitatum_, n. sp.

Both arms equal, club-shaped, three times as long as broad, in the outer distal half thickened, three times as broad as at the narrow base; on the distal end of each arm a strong, angular, terminal spine. (The form of the arms like that of _Stephanastrum capitatum_, Pl. 44, fig. 1.)

_Dimensions._--Radius of each arm 0.22, basal breadth 0.02, terminal breadth 0.06.

_Habitat._--Equatorial Atlantic, Station 347, surface.

6. _Amphibrachium armatum_, n. sp.

Both arms equal, four times as long as broad, in the thickened distal part twice as broad as at the base, thorny, with twenty to thirty larger spines on the distal end, and a very large pyramidal spine in the longitudinal axis. (The form of the arms like that of the odd arm in _Euchitonia carcinus_, Pl. 43, fig. 10.)

_Dimensions._--Radius of each arm 0.24, basal breadth 0.03, distal breadth 0.06.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

Subgenus 3. _Amphibrachoma_, Haeckel.

_Definition._--Both arms of different size or form, without terminal spines.

7. _Amphibrachium indicum_, n. sp.

Both arms club-shaped, but very different in size and form; larger arm three times as long and twice as broad as the smaller arm; the larger with nine joints slowly increasing in size, the smaller with four joints, rapidly increasing; the terminal joint three times as broad as the basal. Distal end blunt, rounded, without spines.

_Dimensions._--Radius of the larger arm 0.24, of the smaller 0.08; distal breadth of the former 0.06, of the latter 0.03; basal breadth 0.015.

_Habitat._--Indian Ocean, Ceylon, Haeckel, surface.

Subgenus 4. _Amphibrachura_, Haeckel.

_Definition._--Both arms of different size or form, with terminal spines.

8. _Amphibrachium clavula_, n. sp.

Both arms different in size and form; larger arm club-shaped, four times as long as broad, at the distal end three times as broad as at the base, and twice as long as the smaller arm, which resembles a stalked knob, with thin basal peduncle and spherical distal part. Ends of the two arms {519}thorny (with numerous smaller, and three to five larger spines); one very large conical terminal spine on each pole of the main axis.

_Dimensions._--Radius of the larger arm 0.3, of the smaller 0.15; distal breadth of the former 0.06, of the latter 0.04; basal breath 0.02.

_Habitat._--South Atlantic, Station 333, surface.

Genus 224. _Amphymenium_,[263] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with two simple, undivided, chambered arms, opposite in one axis, connected by a patagium.

The genus _Amphymenium_ differs from the preceding _Amphibrachium_, its ancestral form, by development of a patagium or connecticulum between both arms. This forms a latticed or more spongy envelop, which surrounds either the middle part of the shell, or the whole shell with exception of the distal ends of both arms. If the envelop become very spongy, the shell may be confounded with the cylindrical Ellipside _Spongocore_ (nearly allied to _Spongurus_); possibly also _Ommatogramma_ of Ehrenberg belongs to this genus.

Subgenus 1. _Ommatogramma_, Ehrenberg (?).

_Definition._--Both opposite arms of the same size and form, blunt, without terminal spines.

1. _Amphymenium pupula_, n. sp. (Pl. 44, fig. 8).

Both arms equal, twice as long as broad, three-jointed; the terminal joint egg-shaped, as large as both other joints together; distal end rounded, blunt. Patagium nearly complete, enveloping the arms with exception of the distal end. Perimeter nearly spindle-shaped.

_Dimensions._--Radius of each arm 0.17, greatest breadth 0.06; transverse breadth of the patagium 0.13.

_Habitat._--Pacific, central area, Station 273, depth 2350 fathoms.

2. _Amphymenium naviculare_, Haeckel.

? _Ommatogramma navicularis_, Ehrenberg, 1872, Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, p. 317; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf.
vi. fig. 7.

Both arms equal, three times as long as broad, spongy, not jointed; distal end a little club-shaped, blunt. Patagium nearly complete, enveloping the arms with exception of the distal end. Perimeter nearly lanceolate. The imperfect diagnosis and figure of Ehrenberg make it doubtful {520}whether this species belongs to the Porodiscida (_Amphymenium_) or to the Spongodiscida (_Spongobrachium_) or perhaps to the Spongurida (_Spongocore_).

_Dimensions._--Radius of each arm 0.1, greatest breadth 0.03; transverse breadth of the patagium 0.05.

_Habitat._--North Pacific, Californian Sea, depth 2600 fathoms, Ehrenberg.

3. _Amphymenium zygartus_, n. sp. (Pl. 44, fig. 7).

Both arms equal, four times as long as broad, with seven to eight joints, slowly decreasing in size towards the blunt end. Patagium incomplete, protecting only the middle part of the shell on both sides; on each side two parallel lattice-plates, connected by transverse radial beams, perpendicular to the surface. Perimeter nearly rectilinear. (Resembles much certain forms of _Zygartus_, Pl. 40, but is a true Discoid, no Prunoid.) Compare also Pl. 45, fig. 8.

_Dimensions._--Radius of each arm 0.2, greatest breadth 0.05; transverse breadth of the patagium 0.11.

_Habitat._--Pacific, central area, Station 271, surface.

4. _Amphymenium monstrosum_, n. sp. (Pl. 44, fig. 11).

Both arms equal, little longer than broad, with six to seven convex joints. The axis of both arms is not common and straight, as in all other species of this genus, but broken, therefore the incomplete patagium, which envelops only two to three joints of the arms, is on one side convex, on the other side concave; it is formed by a simple lattice-plate, connected with the arms by numerous radial beams. This anomalous form, seen only once, may perhaps be a monstrosity of _Euchitonia_.

_Dimensions._--Radius of each arm 0.12, greatest breadth 0.06; transverse breadth of the patagium 0.13.

_Habitat._--South Pacific, Station 290, surface.

Subgenus 2. _Ommathymenium_, Haeckel.

_Definition._--Both opposite arms of the same size and form, armed at the distal end with terminal spines.

5. _Amphymenium amphistylium_, n. sp. (Pl. 44, fig. 9).

Both arms equal, three times as long as broad, thickened towards the truncated distal end, and armed with a strong pyramidal terminal spine. Each arm with seven joints, separated by convex, transverse septa, and halved by a radial beam lying in the longitudinal axis. Patagium incomplete, cylindrical, enveloping only the middle part of the shell.

_Dimensions._--Radius of each arm 0.18, greatest breadth 0.06; transverse breadth of the patagium 0.08.

_Habitat._--North Atlantic, Station 354, surface.

{521}6. _Amphymenium fusiforme_, n. sp.

Both arms equal, lanceolate, three times as long as broad in the width, with seven to eight joints. Distal end pointed, armed with a strong conical terminal spine. Patagium complete, enveloping the whole shell with exception of the terminal spines. Whole form spindle-shaped.

_Dimensions._--Radius of each arm 0.2, greatest breadth 0.07; transverse breadth of the patagium 0.15.

_Habitat._--South Atlantic, Station 330, surface.

Genus 225. _Amphirrhopalum_,[264] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with two chambered arms, opposite in one axis, without a patagium; one arm or both forked at the distal end.

The genus _Amphirrhopalum_ differs from _Amphibrachium_, its ancestral form, by bifurcation of the distal ends of the arms, which may affect either both arms, or only one of them.

Subgenus 1. _Amphirrhopalium_, Haeckel.

_Definition._--Both opposite arms of similar size and form, with blunt branches, without terminal spines.

1. _Amphirrhopalum ximorphum_, n. sp.

Both arms equal, in the proximal half simple, in the distal half forked, with six to seven transverse septa; distal end of each branch blunt, without terminal spine, somewhat broader than the base of the whole arm. Axis of the branches concavely curved. (Resembles _Amphicraspedum maclaganium_, Pl. 45, fig. 11, but wants the patagium.)

_Dimensions._--Radius of the arms 0.18, basal breadth 0.065; terminal breadth of each branch 0.075.

_Habitat._--North Pacific, off Japan, Station 240, surface.

2. _Amphirrhopalum amphidicranum_, n. sp.