ECHINOIDEA. II. 



45 



thus being number 5; in another case it is the plate V. b. 5 which is expanded, but the 4th plate just 

 touches the episternal plate 5. a. 3. Now on the Figure 2, PI. XXX. a of the Challenger-Echinoidea 

 it is seen to be the 5th or 6th plate which thus expands; neither is the fig. 9 on this plate in accord- 

 ance with the rule. This would seem to prove that the specimens represented in these figures cannot 

 be naresianus (Agassiz also doubts himself, whether the specimen represented in Figs, i 6 is cor- 

 rectly referred to U. naresianus (Chall.-Ech. p. 147) and since in U. giganteus it is the 6th ambula- 

 cral plate which expands, the suggestion lies at hand that they belong perhaps to this species. On a 

 careful examination of the specimen represented in Figs, i 6, however, I find the plastron of the 

 same structure as in naresianus, the 4th ambulacral plate being expanded. The difference in the struc- 

 ture of the plastron from the normal condition shown in PL XXX. a Fig. 2 is due to incorrect drawing. 

 (It is beyond doubt that it is really the specimen, figured in the quoted figures, which I have examined; 

 it quite agrees otherwise with the figures, and also the size agrees -- it is ca. 28 mm in diameter, and 

 the figures represent it twice magnified ; it is from St. 146.) That this specimen is only an abnormal 

 U. naresianus, as stated by Agassiz (op. cit. p. 148), I think quite certain. As for the figure 9. 

 PL XXX. a. it is so indistinct in the delimitation of the plates that it is certainly allowable to suggest 

 that it is also incorrectly drawn. 



The specimens from St. 302, which I have likewise examined in the British Museum, differ 

 somewhat from the Atlantic specimens of naresianus in regard to the pedicellarise. The ophicephalous 

 pedicellarise (PL IX. Fig. 4) have shorter and broader valves, and likewise the coarse form of tridentate 

 pedicellariae (PL IX. Fig. 21) is somewhat different, being more slender than in the Atlantic specimens. 

 On the other hand, the globiferous pedicellarise are like those of naresianus, and likewise the structure 

 of the plastron is the same. Perhaps on a careful comparison with the Atlantic specimens this form 

 will prove to be a distinct species; the differences in the pedicellariae pointed out here are, however, 

 certainly too small for founding a new species upon them alone. 



The geographical and bathymetrical distribution of U. naresianus has thus to be somewhat 

 restricted; it is stated in the Challenger-Report (p. 218) to occur, from Marion Island to Kerguelen 

 to Australia; Juan Fernandez to Straits of Magellan; Caribbean Islands, at a depth of 1200 1800 

 fathoms (on p. 255 it is stated to occur at 422 fathoms at the Caribbean Islands). In reality the species 

 is as yet known with full certainty only from the Atlantic and off South Africa (Marion Island), from 

 depths of 422 1715 fathoms. 



A few remarks may be given here on Urcchinus giganteus Ag., which I had occasion to exa- 

 mine in the U. S. National Museum, only some fragments, to be sure, but determined by Professor 

 Agassiz himself. (<?Albatrosss 81.3431.) The structure of the test has been most carefully worked out 

 by Agassiz (Panamic Deep-Sea Echini, p. 152), but no mention is made there of the pedicellarise. 

 They prove to be very characteristic. The globiferous pedicellariae (PL IX. Figs. 2, 6) differ considerably 

 from those of naresianus; the blade is an elongate, rather thick tube, which has a large, oval opening 

 on the inside at the point, with i 3 slender teeth on each side at the outer end; the basal part is 

 comparatively small. The valves are invested with a thick skin, not especially thickened over the 

 point, as is the case in naresianus. (Probably there will be some kind of glands within the large 

 tube). The stalk as in naresianus. The ophicephalous pedicellariae are somewhat more elongate, the 



