36 DE. p. H. CABPENTEK ON CERTAIN" POINTS 



compariug thein witli tliose of Crinoids. Perhaps they would 

 have been less so bad they been acquainted witb. tbe structure of 

 the genus Acrocrinus, in which the radials are separated from the 

 basals by three or four rings o£ plates, and may also be separated 

 laterally as well. Variations from the primitive arrangement of 

 the same kind, though scarcely greater in degree, occur among 

 the Ophiurids ; but I do not see that this in any w\ay affects the 

 homologies of the basal and radial plates in the Ophiurids and 

 Crinoids respectively. 



I am glad to find, however, that the Sarasins admit the com- 

 plete correspondence between the oral system of Psolus and that 

 of Hyocrinus. But they do not seem to be aAvare that this was 

 described by myself twelve years ago*, when I also pointed out 

 that oral plates corresponding to those of the Neocrinoids are 

 developed in two Holothurian larvse, besides persisting in the 

 adult Psolidse. We have seen that they are present in many 

 Cystids, and they are also present in some Blastoids {Elceacrinus). 

 Gotte t and Bury % have pointed out that they are the actinal 

 representatives of the basals in the Pentacrinoid larva; and as 

 Wachsmuth § took the same view of the so-called proximals in 

 the summit of the Palseocrinoids, I was led to regard these also 

 as orals ||, an opinion which, as we have already seen, the American 

 authors have at last adopted^. I liave pointed out above how 

 this doctrine is strengthened by the correspondence between 

 basals and orals in the non-pentamerous forms, such as Cari/ocrinus 

 and Hldzocriniis, a fact which I commend to the notice of the 

 Sarasins. The mouth-plates of Ophiurids are now generally 

 recognized as orals, and there are strong reasons for regarding 

 the so-called odontophores of Asterids as belonging to the same 

 category**. Their presence in the Urchins is doubtful, except, 



* " On the Apical and Oral Systems of the Echiuodermata, Part II.," Quart. 

 Journ. Micr. Sci. 1879, vol. xix. p. 191. 



t " Vergleichende Eutwictelungsgescbiehte der Comatula Mediterrauea/' 

 Archiv f. niikr. Anat. 1876, Ed. xii. p. 621. 



X Phil. Trans. 1888, B, p. 270. 



§ " Notes on the Internal and External Structure of Palseozoic Crinoids," 

 Amer. Journ. Sci. 1877, vol. xiv. p. 189. 



II Quart. Journ. Micr. Sci. 1879, vol. xix. p. 182. 



^ Proc Acad. Wat. Sci. Philad. 1888, p. 348. As already noted, this state- 

 ment refers to the four anterior proximals only. 



** See Sladen, " On the Homologies of the Primary Larval Plates in the Test 

 of Brachiate Echinoderms," Quart. Journ. Micr. Sci. 1884, vol. xxiv. p. 40. 

 See also the postscript to this paper, injra, pp. 43, 44. 



