1. Mesocena circulus, Ehrenberg.

Rings of the skeleton circular, smooth or slightly denticulate on the outer margin, without spines. This simple form is probably the ancestral form of the Dictyochida.

Dimensions.—Diameter of the rings 0.02 to 0.03, thickness of the hollow rod 0.001 or less.

Habitat.—Fossil in Tertiary rocks of Barbados and of the Mediterranean (Ægina, Greece; Caltanisetta, Sicily).

2. Mesocena annulus, n. sp.

Rings of the skeleton elliptical, smooth or slightly denticulate on the outer margin, without spines. This species is possibly identical with Mesocena crenulata of Ehrenberg, of which, however, no figure is given. The major axis of the ellipse is one and a half times as long as the minor.

Dimensions.—Diameter of the rings in the major axis 0.03, in the minor 0.02; thickness of the bars 0.002.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

3. Mesocena diodon, Ehrenberg.

Rings of the skeleton elliptical, smooth, with two opposite spines on the poles of the major axis, which is about one and one-third as long as the minor axis.

Dimensions.—Diameter of the rings in the major axis 0.04, in the minor 0.03; length of the spines 0.01.

Habitat.—Fossil in Barbados, and in North America (Virginia).

4. Mesocena triangula, Ehrenberg.

Rings triangular, with small peripheral thorns, and three larger teeth on the corners of the equilateral triangle.

Dimensions.—Diameter of the rings 0.03 to 0.05, length of the spines 0.01.

Habitat.—Fossil in Tertiary deposits of the Mediterranean; Caltanisetta, Sicily (Ehrenberg, Stöhr).

5. Mesocena quadrangula, Ehrenberg.

Rings square, with four radial spines on the corners of the square. Ehrenberg has given only the name of this species, but neither diagnosis nor figure. I think it may be identical with the species described, which I found in the North Atlantic.

Dimensions.—Diameter of the rings 0.02 to 0.025, length of the spines 0.007 to 0.01.

Habitat.—North Atlantic, Færöe Channel, Gulf Stream (John Murray), depth 600 fathoms.

6. Mesocena elliptica, Ehrenberg.

Rings elliptical or ovate, with four peripheral spines which lie in two diameters, perpendicular to one another, two opposite in the major, the two others in the minor axis of the ellipse.

Dimensions.—Diameter of the rings 0.015 to 0.03, length of the spines 0.005.

Habitat.—Fossil in Tertiary rocks of the Mediterranean (Placca di furni, from Zante, Greece); Caltanisetta, Sicily.

7. Mesocena pentagona, n. sp.

Rings regularly pentagonal, with smooth straight bars, and with five short and straight radial spines on the five corners.

Dimensions.—Diameter of the rings 0.02, length of the spines 0.005.

Habitat.—Fossil in Barbados.

8. Mesocena hexagona, Haeckel.

Rings regular, hexagonal, with six radial spines on the six corners (sometimes between the usual six-radiate rings of one and the same individual are intermingled single rings with five or seven spines).

Dimensions.—Diameter of the rings 0.025 to 0.03, length of the spines 0.007 to 0.01.

Habitat.—Mediterranean, Krim (Ehrenberg), Corfu (Haeckel).

9. Mesocena octogona, Ehrenberg.

Rings regular, octagonal, with eight radial spines on the eight corners of the ring (sometimes between the common octoradiate rings single rings with seven or nine teeth are intermingled in one and the same calymma).

Dimensions.—Diameter of the rings 0.02, length of the spines 0.005.

Habitat.—Tropical Pacific; Peru, Ehrenberg; Station 272 to 274, surface.

10. Mesocena bisoctona, Ehrenberg.

Rings circular, with sixteen teeth; eight stronger teeth regularly disposed on the outer margin, alternating with these eight smaller teeth on the inner margin.

Dimensions.—Diameter of the rings 0.02, length of the outer spines 0.005.

Habitat.—Fossil in Guano from Peru and South Africa, also in Barbados.

11. Mesocena stellata, n. sp. (Pl. 101, fig. 9).

Rings circular, with sixteen teeth regularly disposed on the outer margin of the rings, eight stronger teeth alternating with eight smaller.

Dimensions.—Diameter of the rings 0.03, length of the larger spines 0.01.

Habitat.—Central area of the Pacific, Station 270, depth 2925 fathoms.

Genus 662. Dictyocha,^[280] Ehrenberg, 1838, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 128.

Definition.—Cannorrhaphida with a skeleton composed of annular pieces, which are fenestrated by one or more arches, arising on one side of the simple ring, but do not form a truncated pyramid (therefore no apical ring).

The genus Dictyocha is a very remarkable and interesting form of Phæodaria, which has had a curious history. Ehrenberg, who first observed single pieces of it fossil in Tertiary rocks, supposed it to be the siliceous carapace of a Diatom, and gave it the following diagnosis: "Dictyocha, e familia Bacillariorum. Lorica simplex univalvis silicea, laxe reticulata aut stellulata" (loc. cit.). In my Monograph (1862, p. 271), I placed it in the class Radiolaria, supposing that it might be a simple form of Acanthodesmida, having found only isolated siliceous pieces. Afterwards (in 1879) Richard Hertwig observed the entire living body, and demonstrated that the hollow siliceous pieces are scattered in great numbers around a tripylean central capsule, which exhibits all the essential characters of Phæodaria (Organismus d. Radiol., 1879, p. 89). Hertwig describes the position of the numerous siliceous pieces in the surface of the extracapsular jelly-sphere so densely aggregated, that they touch one another and produce the appearance of a reticulated sphere. In two specimens, which I observed living (Pl. 101, fig. 10), and in numerous complete specimens which I found in the collection of the Challenger, the number of the siliceous pieces was much smaller, and they were scattered irregularly in the surface of the alveolate jelly-sphere, being separated by wide and unequal intervals. The regular position seems to be that the basal rings lie tangentially in the spherical surface of the calymma, whilst the bars of the reticulum are directed outwards, and the apical spine radially in centrifugal direction. Very often two pieces are united by their basal rings in such a manner that they form a little spheroidal fenestrated body (as in Distephanus, Stöhr; compare p. 1550). The characteristic reticular skeleton-pieces of Dictyocha must be derived from Mesocena; from its simple siliceous ring (on one side of its plane), arise two, three, or four (rarely more) bars, which become united to a loose framework (with two, three, or four meshes). When this network assumes the form of a truncated pyramid (with a central mesh on the apex), Dictyocha passes over into Distephanus. From the corners of the original basal ring several radial spines usually arise in a centrifugal direction, and on the sides of these sometimes small teeth or thorns also run in a centripetal direction. The number of the meshes and the separating rods is usually four, more rarely two or three. The hollow rods are very thin, either cylindrical or prismatic. As the ascending rods alternate regularly with the corner-spines of the basal ring, we may call the latter perradial, the former interradial. Ehrenberg has distinguished in his genus Dictyocha not less than fifty species, thirty-five living and twenty-five fossil (ten species both living and fossil). The greater part of these cannot be retained, as they are only slight varieties or abnormalities of single pieces of the skeleton, such as very frequently occur associated with the common regular forms in one and the same individual. Such abnormal species are, e.g., Dictyocha abnormis, Dictyocha binoculus, Dictyocha bipartita, Dictyocha haliomma, Dictyocha hexathyra, Dictyocha septenaria, &c. One species (Dictyocha splendens), is the fenestrated calcareous body of a Holothurian. Of some other species Ehrenberg has only given the name, but neither a description nor a figure (e.g., Dictyocha borealis, Dictyocha cenostephania, Dictyocha compos, Dictyocha coronata, Dictyocha socialis, Dictyocha specillum). A number of other species must be placed in the genera Distephanus and Cannopilus, so that only eight of his species of true Dictyocha remain.

1. Dictyocha navicula, Ehrenberg.

Each individual ring elliptical or oblong, with one transverse arch in the shorter axis, which bisects it into two meshes. No spines or teeth.

Dimensions.—Diameter of the ring 0.02, of the bars 0.001.

Habitat.—Fossil in Tertiary deposits, Barbados, Sicily, &c.; living in the Atlantic, Stations 352, 354, and off Bermuda, surface.

2. Dictyocha quadrata, Ehrenberg.

Each individual ring square or rhomboid, with one transverse arch in the shorter axis, forming two meshes. Two peripheral opposite spines on the poles of one axis.

Dimensions.—Diameter of the ring 0.015.

Habitat.—Atlantic, Bermuda Islands; fossil in Barbados.

3. Dictyocha pons, Ehrenberg.

Each individual ring elliptical or oblong, with one transverse arch in the shorter axis, forming two meshes. Four peripheral spines, on the poles of the longer and of the shorter axis. (The individual abnormality, figured as Dictyocha tripyla, loc. cit., Taf. xxi. fig. 41, has the transverse arch bifid at one end, therefore three meshes result; this forms an interesting transition to Dictyocha fibula.)

Dimensions.—Diameter of the ring 0.01, of the bars 0.001.

Habitat.—Fossil in Tertiary rocks, Oran, Africa.

4. Dictyocha triommata, Ehrenberg.

Each pileated piece of the skeleton is a small three-sided pyramid, the sides of which form three triangular meshes; the three edges between them are three curved interradial beams, united in the centre (the apex of the pyramid). Alternating with these, three horizontal, perradial, centrifugal spines start from the base.

Dictyocha trigona, Zittel, 1876 (L. N. 29, p. 83, Taf. ii. fig. 6), is an interesting Cretaceous species, perhaps a variety of Dictyocha triommata.

Dimensions.—Diameter of the basal triangle 0.01, of the three meshes 0.005.

Habitat.—Fossil in different Tertiary deposits (of Sicily, Greece, North America); living in the Central Pacific, Stations 270 to 272, depth 2600 to 2925 fathoms.

5. Dictyocha tripyla, Ehrenberg.

Each pileate piece of the skeleton is a small three-sided pyramid, similar to that of Dictyocha triommata, but differs from it in the possession of three small perpendicular teeth, which are directed downwards and start from the basal ring near the origin of the three horizontal spines.

Dimensions.—Diameter of the triangular basal ring 0.015, of the three meshes 0.007.

Habitat.—Fossil in Tertiary deposits. North Africa (Oran), Sicily (Caltanisetta).

6. Dictyocha medusa, n. sp. (Pl. 101, figs. 13, 14).

Each pileated piece of the skeleton has four equal, cruciate, triangular meshes. From the four corners of the square basal ring proceed four perradial horizontal spines, and between these four interradial curved bars, which correspond to the edges of a four-sided pyramid, arise from the centre of the four sides and become united in the centre (on the apex of the pyramid). No apical spine.

Dimensions.—Diameter of the basal ring 0.02, of the four meshes 0.01.

Habitat.—Central area of the Pacific, Station 272, depth 2600 fathoms.

7. Dictyocha staurodon, Ehrenberg.

Each pileated piece of the skeleton is a small, regular, four-sided pyramid, similar to the foregoing species. It differs from Dictyocha medusa in the development of a vertical apical spine, and of four small centripetal teeth, which start from the inside of the basal square, between the four perradial spines and the four ascending interradial beams.

Dimensions.—Diameter of the basal ring 0.025, of the meshes 0.01.

Habitat.—Fossil in Tertiary rocks; Tripel of Richmond, Virginia (Ehrenberg); Barbados, (Haeckel); living in the Tropical Atlantic, Station 347, surface.

8. Dictyocha fibula, Ehrenberg.

Each pileated piece of the skeleton stirrup-shaped, with two pairs of meshes, and a square basal ring, the four corners of which are prolonged into four perradial spines. Between the latter four interradial beams arise from the sides in pairs, and the two pairs are connected by a diagonal arch. Therefore the two opposite meshes are larger and pentagonal, the other two meshes (alternating with these) are smaller and square. No vertical spine on the apex.

Dimensions.—Diameter of the basal square ring (diagonal) 0.01 to 0.02, of the meshes 0.005.

Habitat.—Fossil in different Tertiary rocks (Barbados, Oran, Greece, Sicily, &c.), Ehrenberg.

9. Dictyocha messanensis, Haeckel.

Each pileated piece of the skeleton stirrup-shaped, very similar to Dictyocha fibula, but distinguished by a vertical apical spine in the centre of the transverse arch, which connects the two pairs of ascending bars.

Dimensions.—Diameter of the basal ring 0.02 to 0.03, of the meshes 0.01 to 0.016.

Habitat.—Mediterranean (Messina), North Atlantic (Canary Islands), Station 354, surface.

10. Dictyocha epiodon, Ehrenberg.

Each pileated piece of the skeleton stirrup-shaped, with four paired meshes similar to the hats of Dictyocha fibula, but distinguished by four small centripetal thorns, which start from the inside of the basal ring, at the side of the four ascending beams. No apical spine.

Dimensions.—Diameter of the basal ring 0.03, of the meshes 0.01.

Habitat.—Fossil in Tertiary rocks of North America (Miocene Tripel of Richmond, Virginia, &c.).

11. Dictyocha stapedia, n. sp. (Pl. 101, figs. 10-12).

Each pileated piece of the skeleton stirrup-shaped, with four paired meshes, similar to the hats of Dictyocha fibula and Dictyocha messanensis, but distinguished by four small centripetal teeth, which start from the inside of the basal ring, at the side of the four ascending beams. In the centre of the diagonal arch arises a vertical apical spine (differing from Dictyocha epiodon). This species seems to be the most common of the living forms and widely distributed over all warmer seas. I observed in Ceylon, taken on the surface, the living specimen figured in Pl. 101, fig. 10, the numerous spicula were irregularly scattered over the spherical surface of the alveolate calymma. Other specimens occur in various preparations of the Challenger collection, from the Atlantic and the Pacific. The majority of the siliceous little hats exhibited the stirrup-form shown in fig. 11, and many were united in pairs, forming a twin-piece (fig. 12). Intermingled with these are found some irregular forms, representing the specific form of some allied species, viz., Dictyocha speculum, Dictyocha staurodon, Dictyocha epiodon and Dictyocha messanensis.

Dimensions.—Diameter of the basal ring 0.015 to 0.03, of the meshes 0.005 to 0.012.

Habitat.—Cosmopolitan; Atlantic, Pacific, Indian Ocean, in the Tropical and warmer regions; Stations 159, 244, 266-272, 318, 352, &c.

12. Dictyocha rhombus, n. sp.

Each pileated piece of the skeleton stirrup-shaped, similar to Dictyocha stapedia, with four paired meshes. It differs from the latter in the rhomboid form of the basal ring and the larger size of the two opposite meshes, which are two to three times as large as the two others. Therefore the four centripetal teeth of the basal ring do not stand in the four single meshes, but in pairs only in the two larger meshes.

Dimensions.—Diameter of the basal ring 0.02, of the meshes 0.005 to 0.01.

Habitat.—North Atlantic; Færöe Channel, Gulf Stream, depth 50 to 600 fathoms, John Murray.

Genus 663. Distephanus,^[281] Stöhr, 1880, Palæontogr., vol. xxvi. Taf. ii. p. 121.

Definition.—Cannorrhaphida with a skeleton composed of pileated pieces, each of which is a small truncated pyramid with one girdle of meshes (the apical ring being simple).

The genus Distephanus was founded in 1880 by Stöhr (loc. cit.) for a single twin-piece of the skeleton of Dictyocha speculum. Among the common fossil forms of this species he once found in the Tertiary rocks of Caltanisetta, Sicily, a single piece (loc. cit., Taf. vi. fig. 9), which seemed to be composed of two equal pieces so united that they formed a little sphere with fourteen meshes; on each pole of the sphere lies a central hexagonal mesh surrounded by six pentagonal meshes, and from the six corners of the equatorial ring arise six centrifugal spines. No doubt this was a mistake, and the apparent little sphere was one of the above mentioned twin-forms, composed of two separate hexagonal truncated pyramids, which were loosely connected by their basal rings. I have often seen such twin-pieces of Dictyocha speculum and of other species (Pl. 101, fig. 12, Pl. 114, fig. 8), and was always able to separate the two loosely connected halves of the bivalve shell by slight compression.

The genus Distephanus of Stöhr, therefore, is nothing other than the Dictyocha of Ehrenberg. But I think it is more convenient to retain the name Distephanus for those forms of Dictyocha which possess a simple apical mesh surrounded by a ring of lateral meshes, and in which each piece of the skeleton forms a small truncated pyramid. The basal plane of this pyramid is marked by the original basal ring (Mesocena), the truncated upper plane by the parallel apical ring, and the edges of the pyramid by the rising bars which connect both rings. In this sense, so far as the two rings lying in parallel planes are concerned, the term Distephanus is correct (but not in the original sense of Stöhr). The number of the rising bars between the two rings varies from four, five, six to eight or more. It seems rather constant in each species, so that all the pieces of the skeleton of one specimen possess either four or six or eight lateral meshes, &c. But sometimes individual irregularities occur. In the majority of species each skeleton-piece is armed with spines. Usually a radial horizontal spine starts centrifugally from each corner of the basal ring, and on the side of this a small tooth or thorn often starts centripetally or downwards. In the twin-pieces, where the two basal rings are united, these teeth catch into one another. In some species upper spines also occur, starting from the corners of the apical ring. The perradial spines of the corners of the basal ring alternate regularly with the interradial ascending bars, which bisect the sides of the ring, as in Dictyocha.

1. Distephanus crux, Haeckel.

Each pileated piece of the skeleton exhibits four pentagonal lateral meshes around one square central mesh, and is composed of two horizontal square rings; the smaller upper square is connected with the larger lower square by four ascending interradial beams, which start from the corners of the former and bisect the sides of the latter; from the corners of the basal ring arise four short perradial spines.

Dimensions.—-Diameter of the basal ring 0.02 to 0.03, of the apical ring 0.008.

Habitat.—-Tropical Atlantic, Station 347, surface; fossil in Tertiary deposits of the Mediterranean (Sicily, Oran).

2. Distephanus mesophthalmus, Haeckel.

Each pileated piece of the skeleton exhibits four lateral meshes around the central mesh, and is composed of two parallel horizontal square rings, like those of Distephanus crux, but distinguished from this by eight short teeth, four centripetal on the larger lower ring and four perradial centrifugal on the smaller upper ring.

Dimensions.—Diameter of the basal ring 0.03, of the apical ring 0.015.

Habitat.—Fossil in Tertiary rocks of Sicily, Caltanisetta (Ehrenberg); living in the Central Pacific, Station 270 to 272, surface.

3. Distephanus stauracanthus, Haeckel.

Each pileated piece of the skeleton exhibits four lateral meshes around the central mesh, and is composed of two horizontal rings, which are connected by four perradial beams arising from the corners of the upper and smaller square ring. Lower ring octagonal, with eight peripheral adradial spines, and with four interradial centripetal teeth on the inside.

Dimensions.—Diameter of the basal ring 0.03, of the apical ring 0.004.

Habitat.—Fossil in Tertiary rocks of North America (Hollis Cliff, Virginia; Norwich, Connecticut).

4. Distephanus asteroides, n. sp.

Each pileated piece of the skeleton exhibits five lateral meshes around the central mesh (or the upper ring). Five peripheral spines (on the corners of the lower ring) simple, not articulated.

Dimensions.—Diameter of the basal ring 0.02, of the apical ring, 0.007.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

5. Distephanus pentasterias, Haeckel.

Each pileated piece of the skeleton exhibits five lateral meshes around the central mesh (or the upper ring). Five peripheral spines (on the corners of the lower ring) articulated, triangular, with three distinct joints (tapering towards the distal end).

Dimensions.—Diameter of the basal ring 0.012 to 0.018, of the apical ring 0.002 to 0.003.

Habitat.—Cosmopolitan; living in the depths of the Atlantic and Central Pacific, Stations 247, 270 to 272, depths 2530 and 2600 to 2925 fathoms; fossil in Tertiary deposits (Tripel of Caltanisetta, Sicily; Richmond, Virginia).

6. Distephanus speculum, Haeckel.

Each pileated piece of the skeleton is a truncated, six-sided pyramid, and composed of two regular hexagonal rings which lie in parallel plains, and are connected by six ascending interradial beams; these start from the corners of the upper smaller ring and bisect the sides of the lower larger ring; from the corners of the latter start six perradial centrifugal spines.

Dimensions.—Diameter of the basal ring 0.03, of the apical ring 0.01.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; fossil in Barbados, Sicily, &c.

7. Distephanus ornamentum, Haeckel.

Each pileated piece of the skeleton is a truncated, six-sided pyramid, similar to that of Distephanus speculum, but distinguished by six small (probably vertical) teeth, which start from the inside of the lower (larger) ring, on the sides of the ascending beams.

Dimensions.—Diameter of the basal ring 0.03, of the apical ring 0.015.

Habitat.—Fossil in Tertiary deposits of Sicily, Caltanisetta (Ehrenberg).

8. Distephanus aculeatus, Haeckel.

Each pileated piece of the skeleton is a truncated, six-sided pyramid, similar to that of Distephanus speculum, but distinguished by six small perradial, horizontal teeth, which start from the sides of the upper (smaller) ring.

Dimensions.—Diameter of the basal ring 0.02, of the apical ring 0.008.

Habitat.—Fossil in Tertiary deposits of the Mediterranean; plastic clay of Greece and Sicily; living in the Mediterranean and the Atlantic, Station 352, surface.

9. Distephanus sirius, Haeckel.

Each pileated piece of the skeleton is a truncated six-sided pyramid, similar to that of Distephanus speculum, but distinguished by the six broad, triangular, peripheral spines, which are articulated and connected by a thin siliceous membrane (like a web-membrane); each spine has three articulations (as in Dictyocha pentasterias).

Dimensions.—Diameter of the basal ring 0.02, of the apical ring 0.005.

Habitat.—Fossil in Tertiary rocks (Richmond, Virginia), but also living in the Atlantic Ocean, Gulf Stream, Færöe Channel, John Murray, 1880.

10. Distephanus corona, n. sp. (Pl. 114, figs. 7-9).

Each pileated piece of the skeleton is a truncate six-sided pyramid like that of Distephanus speculum, but differing in the number (twenty-four) of teeth or spines. Six interradial ascending beams connect the two horizontal rings between these, and six nearly vertical spines arise from the perradial corners of the upper hexagonal ring. In the same meridional (perradial) plains six larger spines descend downwards from the corners of the lower larger ring. Between these six descending spines and the six ascending beams arise from the upper edge of the lower ring twelve shorter teeth of unequal size (the right tooth in each pentagonal lateral mesh being smaller and directed upwards, the left tooth being larger and directed nearly horizontally outwards). The lower ring is nearly dodecagonal.

Dimensions.—Diameter of the basal ring 0.025 to 0.03, of the apical ring 0.012 to 0.02.

Habitat.—North-west Pacific, Sea of Japan, Station 231, depth 2250 fathoms.

11. Distephanus octonarius, Haeckel.

Each pileate piece of the skeleton is a truncated eight-sided pyramid, composed of two regular octagonal rings, which lie in parallel plains, and are connected by eight radial beams. From the eight outer corners of the lower ring (or from the eight interradial meshes, between the eight perradial beams) start eight basal centrifugal spines. (This species is similar to Distephanus speculum, but has eight beams instead of six. In single pieces the number of the beams and meshes varies between seven and nine, the constant number being eight.) A seven-rayed variety is Dictyocha septenaria (loc. cit.), a nine-rayed Dictyocha polyactis.

Dimensions.—Diameter of the basal ring 0.02 to 0.03, of the apical ring 0.01 to 0.015.

Habitat.—Fossil in Tertiary rocks (Tripel and Marne from Caltanisetta, Sicily; Oran, Africa); living in the depths of the Atlantic, Station 348, and Pacific, Station 270, &c.

12. Distephanus octogonius, n. sp.

Each pileated piece of the skeleton is a truncated eight-sided pyramid, like that of Distephanus octonarius, but differs from it by having eight short erect teeth, which arise from the corners of the upper smaller ring and lie in the same perradial plains as the eight horizontal spines starting from the corners of the lower larger ring. Ehrenberg has figured only an individual abnormality with seven beams instead of eight, taken from the Antarctic ice; but I found the same form frequent in deep-sea soundings from the Antarctic, almost constantly with eight beams, isolated hats with six, seven, or nine beams being intermingled.

Dimensions.—Diameter of the basal ring 0.02, of the apical ring 0.012.

Habitat.—Antarctic Ocean; in smolten "Pancake-Ice," taken by Sir James Clark Ross in lat. 78° 10' S., long. 162° W. (Ehrenberg); Station 156, depth 1975 fathoms.

13. Distephanus diadema, n. sp.

Each pileated piece of the skeleton is an eight-sided pyramid, like that of the two foregoing species, but differing in the number and distribution of the teeth or spines, which are thirty-two. From the eight corners of the basal ring start eight long, nearly horizontal perradial spines, which bear on each side a smaller, nearly vertically descending spine. From the eight corners of the upper ring ascend also eight perradial spines, alternating with the eight interradial beams, which connect the two rings.

Dimensions.—Diameter of the basal ring 0.04, of the apical ring 0.02.

Habitat.—South Pacific, Station 293, depth 2025 fathoms.

Genus 664. Cannopilus,^[282] n. gen.

Definition.—Cannorrhaphida with a skeleton composed of pileated pieces, each of which is a small truncated pyramid with two girdles of meshes (the apical ring being fenestrated).

The genus Cannopilus represents the most highly developed form of Dictyochida. Each piece of the skeleton is a little fenestrated hat or topped pyramid, as in Distephanus. But the apical mesh is simple in the latter, in the former it is divided into several meshes by bars which start in a centripetal direction from the upper ring. Therefore we find two annular rows of meshes, one above the other; an apical or upper row of smaller meshes and a basal or lower row of larger meshes. In the apex of the little hat is either a central mesh or an apical spine. Other spines arise from the basal ring, as in the former genera. The number of corner-spines on the basal ring is either four, six, or eight (in individual abnormalities also five or seven).

1. Cannopilus superstructus, Haeckel.