354 p. HERBERT CARPENTER. 



(Miller) or "Basis" (Miiller), while the five large plates 

 (3, 3) above it correspond to the Parahasalia of the 

 Palaeozoic Crinoids, the intercalated pieces (4, 4) being 

 considered, as before, as radialia. 



Allman's own view has been accepted by Wyville Thom- 

 son, Dr. Carpenter, M. Sars, and (with some modifications) 

 by Gotte, all of whom have studied the development of 

 Comatula with much care. 



Agassiz^ and Loven, however, prefer to regard the centro- 

 dorsal piece {cd) as a " solidified homologue of the basals 

 of the other Crinoids." There are many and serious ob- 

 jections to this view, which will be discussed at length 

 farther on. 



Correct as AUman undoubtedly was in his analytiis of the 

 calyx of the Pentacrinoid, he was, nevertheless, misled with 

 respect to the homologies of the five large triangular roof 

 plates (or), for he regarded them- as "greatly developed 

 interradialia." 



AVyville Thomson^ and Dr. Carpenter'^ have shown, how- 

 ever, that the true interradials '" of the Pentacrinoid appear 

 between the upper edges of the basals (3, 3), and the lower 

 edges of the roof plates {or), to which they have given the 

 name of Orals from their position around the mouth. On 

 the other hand, both these observers agree with Allman in 

 regarding these interradially disposed oral plates as "in all 

 probability homologous with valve-like plates surrounding 

 the mouth only, in all Crinoidal genera in which they 

 occur.'^^ 



In Haplocrinus these oral plates remain single, but in 

 Coccocrinus, Stephcmocrinus , and Eiicalyptocrinus , they are 

 more or less subdivided. Allman suggests the possibility 

 that the roof of Lageniocrinus is homologous with that of 

 Haplocri7ius and of the young Pentacrinoid." It is difficult 

 to decide whether his, or De Koninck's^ analysis of this 



^ "North American Starfishes," p. 03. 'Memoirs of the Museum of 

 Comparative Zoology at Harvard College,' vol. v, No. 1. 



- Loc. cit., p. 2i5. 



3 " On the Embrjogeny of Autedon rosaceus," ' Phil. Trans.,' vol. civ, 

 p. 540. 



■» " Researches on the Structure, Physiology, and Development of Autc- 

 don rosaceus," part i, 'Phil. Trans.,' vol. clvi, p. 716. 



* These are not precisely homologous with tiic interradials of the FaUeo- 

 crinoidea. 



« 'Phil. Trans.,' vol. civ, p. 542. 



7 Loc. cit., pp. 250, 251. 



^ ' llecherches sur ics Crino'ides du Terrain Carbonifcre dc la Belgique,' 

 p. 188. 



