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.

3. Zygacantha compressa, Haeckel.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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 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.

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.

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.

11. Acanthonia cuspidata, Haeckel.

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.

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.

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.

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.

1. Lithophyllium cruciatum, Haeckel.

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.

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.

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.

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.

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. 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.

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.

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 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.

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.

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.

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.

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, 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.