ECHINONEUS CYCLOSTOMUS. 59 form and large perforations illustrate the variation that obtains in the same specimen.
The open rectangular shape of the first pore in the edge of the actinostome, in a specimen 37 mm. long, from Mauritius, while not of common occurrence, is far from exceptional in specimens from other localities.
Any peripodium would have sufficed to show the variation in shape, but for uniformity the fifth one (PI. 28, figs. 16, 20, 22-24), in the odd anterior ambulacrum of five adult specimens from the Indian, Pacific, and West Indian regions was selected.
THE SPINES.
Plate26,figs.1-15,20-29;Plate27,figs.1-11,14-22,25-34,37-42. There are only two kinds of spines; one on the primary tubercles, the other on the miliaries (Pl. 26, figs. 1-15, 20-29; Pl. 27, figs. 1-11, 14-22, 25-34, 37-42). Those of the primaries are without serrations, some of them on the actinal side, especially those near the oral and anal systems in adult specimens, reach a length of three millimetres or so. The radioles on the abactinal side become stouter with either a blunt or pointed end, and gradually diminish in length until in the apical system they measure less than half a millimetre, and on the madreporic plate not quite one fourth of one.
I have been unable to find any difference between the radioles of specimens from the Pacific or the West Indian regions, excepting a slight individual variation. The base on the longer spines agrees in being higher at one side and thus giving the milled ring a sloping line when seen in profile. The sections of these spines given on Pls. 26, 27, show either about nine or twelve rods in each; exceptionally one or more of these rods (as seen in Pl. 26, figs. 2, 3; Pl. 27, figs. 8, 9, 30, 38, 40), is serrated near the base, or for the whole length. The various forms in the outline of the sectional figures are due to the shape of the rods, which in some spines are semicylindrical, while in others they are much more prominent and deeply separated from each other.
Radioles of the same length, and from the same plate may differ noticeably from each other according as to whether they have a pointed or a rounded tip. This is shown by two spines (PI. 26, figs. 6, 7) from the ambitus, left anterior interambulacrum, of a Pacific specimen, 34 mm. long. A similar difference is also easily seen by comparing two spines from a Barbados specimen, 30 mm. long; one (PI. 27, fig. 18) from the ambitus, right anterior interambulacrum; the other (Pl. 27, fig. 17) from the odd posterior interambulacrum near the anal system.
60 TROPICAL PACIFIC ECHINI.
The spines of the miliaries are serrated, smaller in size and of even diameter up to the distal end where they thicken, and each rod ends in a sharp point. Those found on or close to the actinostome are nearly one millimetre in length, and diminish until in the apical system they are very minute. There are some even on the anal system. ‘The only other form seen was in a Fakarava Island specimen (Pl. 27, figs. 1, 2), where near the actinostome a few of them are lanceolate. The serrations on these spines from near the actinostome, frequently stop short of the distal end in specimens from the Barbados (PI. 27, fig. 15) and Jamaica (Pl. 27, fig. 25).
THE LANTERN AND AURICLES.
Plate11,figs.1,2,7,8;Plate12.
Of the various specimens brought from Port Antonio, Jamaica, a small number were nearly, or but a little over, five millimetres in length; only four, provided with a masticatory apparatus, were under this measurement. Considering that they had been a few days in alcohol, when the preparations were made, they showed the various parts, including the pigmented sack that holds the lantern (PI. 11, figs. 7, 2), very well. The lower end of this sack is probably joined to the buccal membrane by a small neck; it contains a few caleareous particles close to the teeth (Pl. 11, fig. 4). In just what manner this sack passes the pentagonal muscular band of the summit of the lantern, and whether it is connected with the oesophagus which goes through its centre where the compasses meet, could not be ascertained, as the diameter of the lantern was only 1.24 mm. and too fragile for dissection. The calcareous parts of the whole apparatus are fairly solid, and not quite so delicate as the valves of the pedicellariae. To each of the primordial interambulacral plates are attached a pair of strong muscles (PI. 11, fig. 2), each with two branches at the upper end, one of which is fastened to the compass, the other apparently to the brace. The lower end of each half pyramid is also connected by two muscles to the rudimentary auricle, and its ambulacral plate. After being denuded of their spines, the smallest specimens having a lantern, were only 3.70 mm. in length (Pl. 11, fig. 1), and the largest 4.25; in the latter (PI. 11, fig. 8), the volume of the dental apparatus filled about one sixth of the space inside the test. The next available size was 5.16 mm. in length (Pl. 11, fig. 9), and lacked not only the masticatory apparatus, but the auricles also (Pl. 11, fig. 10)... It seems very unlikely that *Thestatement(Amer.journ.sci.,1909,ser.4,28,p.490)thatthesmallauriclesarepresentis erroneous.
ECHINONEUS CYCLOSTOMUS. 61 it was shed, or liberated spontaneously. A resorption similar to that which occurs in some parts of the test, appears more probable. In what manner the oesophagus follows this change, and from a tiny tube inserted at the centre of the pyramids, becomes funnel-shaped at its lower end and fastened to, or near the pentagonal nerve and water-vascular canal, which remains permanent on the buccal membrane, is a matter of conjecture.
The auricles are disconnected, minute and flattened to the ambulacral plate (Pl. 11, figs. 5, 6). The largest part of their surface is covered by a muscular attachment. Their resorption is probably contemporary with the dental parts.
The pyramids (PI. 12, figs. 4-8), have deep foramina, a little over one third of the height, are slightly concave on the inside, and somewhat keeled on the outside parallel to the tooth. The adjacent edges are thin, and the corrugations absent. The outline, narrow at the summit, and the lower tapering end, differ considerably from the figure of Discoidea, given by Hawkins (Geol. Mag., new ser. Decade V. April, 1909, 6, p. 148-152, pl.6). The compass (Pl. 12, figs. 11, a. b), is distinctly articulated, and when seen in profile curves at the outer end.
The scapula-shaped epiphyses without being united to the pyramid (PI. 12, figs. 1, 12 a. b), follow the brace horizontally, and are held in place by connecting tissue; this could have been seen (PI. 1, fig. 7), if its minuteness had not prevented removal of the membrane, which would have displaced the parts. The braces do not show any special peculiarity in form.
Seen in profile the strong tooth (PI. 12, figs. 9 a. b. ¢), is distinetly curved with a high keel on the inner face and a shallow groove on the outer. THe ALIMENTARY CANAL.
Plates8-10,Plate11,figs.8,9.
Although the Jamaican specimens were in very good condition for examination, having been in alcohol only a few days, still several important points of anatomical detail remain for future study on living specimens, and the figures given are limited to the alimentary canal, and the associated reproductive organs. The oesophagus rises vertically from the buccal membrane in a thin transparent funnel-shaped tissue, which tapers quickly into a tiny tube (PI. 10, fig. 5), and extends nearly half the height of the test, where close to the insertion of the actinal intestinal appendage it enters the actinal loops of the alimentary canal
62 TROPICAL PACIFIC ECHINI.
(Pl. 10, figs. 1, 2, 4, 5), at a sharp angle. In the young, the oesophagus nearly reaches the madreporic plate, with the axial organ on its right side (PI. 10, fig. 3, Pl. 11, figs. 8, 9). It is held in place with the flat almond-shaped actinal intestinal appendage by a mesentery which is fastened to the abactinal part of the left anterior interambulacrum, close to the odd anterior ambulacrum; this mesentery divides the upper anterior cavity of the test into two open chambers (Pl. 10, fig. 4). The free vertical edge of this mesentery is slightly folded near the genital ducts, broadening as it comes to the buccal membrane where it is apparently connected with the nerve-ring by what may be the lower part of the axial organ (PI. 10, fig. 5). A nerve ascends along the free edge of the mesentery and shortly before reaching the apex, connects with the axial organ. In young specimens, test without spines, 5 mm. long (PI. 9, figs. 4, 5, 6), the general shape of the alimentary canal is nearly like that of the adult. The actinal loop is broad where the oesophagus and actinal intestinal appendage are inserted (Pl. 8, figs. 3-5, Pl. 9, figs. 7, 2), and continues so until in its curve backward and to the right, it passes the right posterior ambulacrum. There it gradually narrows, until it reaches the anterior margin of the right anterior interambulacrum where it curves abruptly upward and becomes the abactinal loop, following the ambitus on the right side of the test. When it reaches the odd posterior interambulacrum, it broadens and has a reéntering curve for passing the rectum (Pl. 8, figs. 3-5), in front of the median line; its outer edge being closer to the test, than that of the actinal loop. In the left anterior interambulacrum, the abactinal loop suddenly tapers (Pl. 8, figs. 4, 5, Pl. 9, fig. 2), passes upward close under the reproductive organs, and becomes tubular. It is held by mesenteries to the abactinal median line of the odd posterior interambulacrum clear to its end at the anal plastron. Posterior to the oesophagus from the buccal membrane (PI. 10, fig. 5), there rises a narrow mesentery which soon turns a half spiral, with its broadest surface attached to the inner edge of the left half of the actinal loop, and to the actinal intestinal appendage; while the narrow part is fastened to the inner edge of the right half of the actinal loop (PI. 8, fig. 3, Pl. 9, fig. 1), as far as the odd anterior ambulacrum. Another mesentery is attached in a similar way to the abactinal loop of the alimentary canal (PI. 10, fig. 4), but is connected with some of the plates of the apical system. Close to the left anterior inner side of the actinal loop, on the mesentery is a brownish pigmented band (PI. 8, fig. 3; Pl. 9, fig. 7), leading from the insertion of the oesophagus, and extending posteriorly. This is probably the accessory intestine.
MICROPETALON PURPUREUM. 63 The tissue of the intestines is generally highly pigmented and smooth, but sometimes contracted with peculiar regularity into surface folds, as seen in Pl. 10, fig. 9. The rectum (PI. 10, fig. 70), in all the specimens examined was contracted lengthwise in long irregular creases.
Satisfactory figures of the nervous and water-vascular systems (Pl. 10, fig. 7), were not obtained, though the ampullae appear to be bilobed, twice as long as wide, and pigmented (PI. 10, fig. 8).
The reproductive organs (PI. 8, fig. 2; Pl. 10, figs. 7, 2), are lacking in the posterior interambulacrum, but show no special peculiarity in their structure. Micropetalon purpureum A. Acassiz and H. L. Ciark.
Plates 29-31.
Unfortunately there is only a single specimen of this species which, although 17 mm. in length may not be fully adult. The general aspect and some of the details are those of Echinonéus. The broad ovoid ambitus, large triangular oral, and oblique anal apertures, recall the specimen of Echinonéus, 16 mm. long, from Florida (PI. 5, fig. 17).
On comparison with a young Echinonéus, 4.40 mm. long, (Pl. 3, figs. 1, 2, Pl. 13, fig. 7, Pl. 14, figs. 7, 2, Pl. 15, fig. 7), from Makemo Island, I find the test frail in both, the ambulacra flattened, and the breadth of the interambulacra at the ambitus in the bivium broader than in the trivium. In Micropetalon the adoral end of the anal opening inclines towards the left posterior ambulacrum, but this may be an individual peculiarity. The size and grouping of the plates on the anal plastron are precisely similar to the same in the young Echinonéus, but being further advanced in age, the anal system has acquired on each side, two additional interradial plates. The oral membrane in each is overlaid with minute caleareous plates, radiating towards the centre. Of the genital plates, three are of about the same size, while the left anterior is smaller. In Micropetalon the genital pores are present, which is not the case in the young Echinonéus. The ocular plates in the bivium are in contact in Micropetalon exactly as in the Echinonéus from Makemo.
The primary tubercles are comparatively few in number, and well separated, being grouped, beginning at about the fourth plate from the actinal system, in two horizontal rows on each plate, or diagonally over the test; each of the last four or more of the abactinal interambulacral plates has only one of these tubercles. Like the young Echinonéus (Pl. 24, figs. 1, 2), Micropetalon has only three series of primary tubercles in the odd anterior ambulacrum. The first tubercle
64 TROPICAL PACIFIC ECHINI.
of the inner series in Echinonéus usually appears first just in front of the fourth tubercle (from the edge of the actinal system) of the outer row; but in Micropetalon it is in front of the second. The mamelon is without perforation, the boss slightly raised, and the scrobicular circle indistinct. Of glassy tubercles there are only a few, mostly near the abactinal system.
Upon comparing the arrangement of the coronal plates in a specimen of Echinonéus, 5.90 mm. long, from Jamiaca (PI. 6, fig. 1), with that of Micropetalon (Pl. 30), I find a notable agreement; and considering the difference in size, it is remarkable that there are nearly the same number of plates in the radii of both.
There were probably three sphaeridia in each ambulacrum, in Micropetalon; those seen were pear-shaped. Of the pedicellariae I found only the ophicephalous, and these show little diversity in form and reveal no special characters. As in Echinonéus, a few spines near the actinal system have serrations which do not continue fully up to the distal end, and the longer spines also vary in having nine or more rods.
One of the notable points is the form of the spicules in the actinal tube-feet; there are four disk plates in each, with yoke-shaped spicules at their inner margins, while the outer edge of the disk generally has a ring of slender spicules slightly bent at both ends. At the ambitus and on the abactinal side near the ocular plates the basal disk has diminished in diameter to about 0.11 mm. with the four disk plates still less developed.
What may especially separate Micropetalon from Echinonéus, is the small low boss of the primary tubercles, that leaves greater intermediary space; while the absence of the thick glossy plates on the oral membrane and the flush poriferous zone with the minute ambulacral pores at the ambitus’ suggest the retention of juvenile characters. The largest pores are in the primordial ambulacral plates, and one or two of the succeeding plates, and are vertically placed; the smallest are arranged diagonally at the ambitus, with a different form of peripodium and of pore opening, which are, however, different from those on the abactinal side towards the ocular plate where the pores are nearly horizontal. The resemblance to Echinonéus and the difference from the adult of that genus which the ambulacral pores of Micropetalon show, are well brought out in the figures (compare PI. 28, figs. 15-18, Pl. 29, figs. 9-12). One specimen of this species was taken during the 1902 cruise of the “‘ Albatross” at Station 3847. Off Lae-o Ka Laan Light, Molokai, Hawaiian Islands, N. 64° 30’, W. 23’. 23-24 fms. bottom of sand and stones.
Thesewereoverlookedwhenthespecimenwasfirststudied(BulletinM.C.Z.,1907,60,p.251).
ECHINONEUS, MICROPETALON. 65 LIST OF SPECIMENS.’
EchinonéuscyclostomusLEsKE.
Numberof|Lengthoftestinmilli- Condition Data specimens | metres | 4 | largest nearly 30 Dry Hawaiian Islands 8 13) 15; 16, 1982052252620 (ee Pacific ?, 1863. J. G. Anthony 4 | 13, 14, 15, 18 fe Kingsmills Islands, Gilbert Islands. A. Garrett 1 | 20 |) Kingsmills Islands 3 | largest about 40 sf Society Islands 7 | 4.40, 10, 12, 14, 15, 18,27 | Aleoholie | Makemo, Paumotu Islands, Oct. 21. ‘Albatross” Exped. 1899-1900. U. S. Nat. Mus. | (5), Mus. Comp. Zodl. (2) 5 | 11, 12, 13, 19, 23 | Fakarava Island, Paumotu Islands. Oct. 12, 1899. “ Albatross’? Exped. 1899-1900, U. 8. } | Nat. Mus. (3) Mus. Comp. Zodl. (2) 4 | 6, 13, 14, 16 Dry | Easter Island, Chile. Dec. 1904, “Albatross” | Exped. 1904-05. U.S. Nat. Mus. (3), Mus. | Comp. Zoél. (1) 1 | 20 ss Australia 2 30, 34 lige ss Lord Howe Island, New South Wales (Littoral) 2 27.5, 28 | Aleoholie | Mauritius, Oct. 13, 1873. Nicholas Pike 2 36, 37 | Dry Mauritius 9 | 5, 8, 9, 11, 15, 26, 28, 29,31) Mauritius. Mrs. Luckock 7 Nile Ay ese Bourbon 1 i ot | Mujeres Island, Yucatan. W. Stimpson 1 16 | Aleoholie | Florida, Carysfort Reef. 1868, L. F. de Pourtalés 2 |20 Dry West Indies 2 | 17, 20 “ Cuba, 1859 1 } 11 Alcoholic | Havana, “Blake,” 1877-78 1 | 26 Dry | Jamaica, Hitchcock 144 | 3.70-28 | Aleoholie | Port Antonio, Jamaica. March, 1909, H. L. | Clark. Mus. Comp. Zool., U. S. Nat. Mus. 29 «| 6-20 Dry | Port Antonio, Jamaica. March, 1909, H. L. Clark 2 |10,15 « Hayti 4 12, 14, 16, 18 s Antilles, 1859 1 14 fs St. Thomas 7 26, 30 | Aleoholic | Barbados (?) U. S. Eclipse Exp. to West Africa | 1989. U.S. Nat. Mus.
Micropetalon purpureum A. AGcassiz and H. L. Cuark. 1 117 Dry Off Lae-o Ka Laan Light, Molokai, Hawaiian Islands. ‘“‘Albatross’” Exped. 1902. U.S. Nat. Mus.
‘AllthespecimensareinthecollectionsoftheMuseumofComparativeZoélogyandtheU.S. National Museum.
66 TROPICAL PACIFIC ECHINI.
SYNONYMICAL LIST.
Ecurnonius Van Phelsum.
1774. Van Phelsum, Brief Zeelglen, p. 32. E. cycLtostomus Leske.
1778. Leske, Addit. Klein, p. 109, pl. 37, fig. 4, 5. 1790. Gmelin, Syst. Nat., 1, pt. 6, p. 3183 (Echinus). 1816. Lamarck, Anim. sans Vert., 3, p. 18. 1819. Blainville, Dict. Sci. Nat., 14, p. 196. 1825. Gray, Thomson’s Ann. Phil., 10, p. 429 (Hchinanaus). 1834. Blainville, Actinologie, p. 212, pl. 16, fig. 5. 1835. Agassiz, Mém. Soc. Sci. Nat. Neuchatel, 1, p. 187. 1842. Desor, Agassiz’s Monog. Echin. Galérites, p. 43, pl. 6, fig. 13-15. 1847. Agassiz, Ann. Sci. Nat., ser. 3, 7, p. 143. 1855. Gray, Catal. Rec. Echin. Brit. Mus., p. 32. 1857. Desor, Synop. Echin. Fossiles, p. 197, pl. 27, fig. 1-3. 1862. Dujardin et Hupé, Echin., p. 545. 1872-73. A. Agassiz, Rev. Echini, p. 117, 550. 1874. Lovén, K. Svenska Veten. Akad. Handl., 11, no. 7, pl. 9, fig. 79-82. 1883. Loriol. Mém. Soe. Phys. Genéve, 28, no. 8, p. 38, pl. 5, f. 3-6. 1894. Anderson, Journ. Asiatic Soc. Bengal, 63, p. 194. 1895. Sluiter, Konin, Zoél. Genoot. Amsterdam, Bijdr. Dierkunde, afley. 1708) pies 1897. Egozcue y Cia, Bol. Com. Mapa Geol. Espafia, 22, p. 48, pl. 15, fig. 5-9.
1899. Anderson, Rept. Marine Surv. India, 1898-99, p. 16. 1907. Mortensen, Danish Ingolf-Exped., 4, pt. 2, p. 184, 193. 1911. Westergren, Ante, p. 44.
E. ovalis Linné.
1753. Linné, Mus. Tessin, p. 114 (Echinus). 1758. Seba, Locup. Rerum Nat. Thes., 3, pl. 10, fig. 7, pl. 15, fig. 30, 33, 34. (Hchinus.)
1771. Knorr, Delic., pl. D. I., fig. 11 (Echinus). E. minor Leske.
1778. Leske, Addit. Klein, p. 110, pl. 49, fig. 8, 9. 1834. Blainville, Actinologie, p. 212. 1842. Desor, Agassiz’s Monog. Echin. Galérites, p. 45, pl. 6, fig. 16.