370 p. HERBERT CARPENTER. 



plates of the Pentacrinoid larva of ComaUda are the true 

 basals which, undergoing much metamorphosis to form the 

 " rosette," become entirely concealed in the adult Comaiula 

 between the radials and the enlarged centrodorsal piece. It 

 is these plates which Loven calls parabasals, and compares, 

 perfectly correctly, to the genital plates of the Urchins and 

 Starfishes. Agassiz, however, calls them interradials,^ thus 

 comparing plates which are essential elements of the Apical 

 systems of both Echini and Starfishes to plates which are by 

 no means universally present in the Crinoids, a proceeding 

 in which he is, I think, scarcely justified. 



Interradials do not occur in the Articulata at all, nor are 

 they present in all the Tessellata, being absent in Hezacrinus 

 (Austin), and in some species of Platycrinus. Even when 

 present (fig. vi, ») they do not form the proximal ring 

 of plates in the apical system as those plates do in the Echini^ 

 to which Agassiz compares them [viz., the genitals (fig. 

 II, 3, 3)], but they intervene between the plates which 

 correspond to the elements of the distal ring of the Echinoid 

 calyx, namely, the radials [= oculars (fig. vi, 4, 4)]. 



Further, if the basals of the PentacrinidcR, Apiocrinida, 

 and the other Articulata collectively represent the central 

 plate of the Apical system, as supposed by Agassiz and 

 Loven, what are the homologues in these Crinoids of the 

 interbrachials of Asterids and the genitals of the Echini? 

 They can have no *' interradial " plates (costals of Loven), 

 for the only plates in their calyx occupying interradial posi- 

 tions are the basals, and these are supposed by Agassiz and 

 Loven to represent the central abactinal plate. They are, 

 however, developed from the homologues of the " interradial " 

 plates (parabasals of Loven) of the larval Comatida, which 

 Agassiz, Loven, and myself all regard as homologous with 

 the genital plates of Echini. Consequently, the views held 

 by Agassiz and Loven involve one of the two following alter- 

 natives : — 



L The interradial elements of the Apical system are 

 absent from the calyx of all the Articulate Crinoids except 



sented, although he professes to have added notes " on the points where 



additions have been made by subsequent investigations." On p. 49 he 



speaks of Loven as " liaving most thoroughly proved the homology of the 



basal and radial plates of Crinoids with their corresponding plates, still 



readily to be traced in the young Starfish, and with their homologies in the 



Apical system of Echini," a statement which 1 cannot endorse. It would 



seem, therefore, that in spite of Dr. Carpenter's proofs to the contrary, 



gassiz adheres to his originally-expressed view that the centrodorsal piece 



Comatula represents the basis of the other Crinoids. 



Loc. cit., pp. 62, 63. 



