310 



P. HERBERT CARPENTER. 



which led me to suggest that these first formed plates between 

 the radials and the dorsocentral of the young Amphiura are 

 the homologues of the Crinoidal basals and of the so-called 

 genitals in Urchins and Asterids ; and the six years' work by 

 myself and others since this suggestion was made has only 

 served to make me more confident of its truth. 



Ludwig gave a very clear description 1 of the appearance of 

 these inter-radially placed basals in the young Amphiura, 

 and he pointed out how at a later stage a set of radially 

 situated plates appears between them and the dorsocentral. 

 He illustrated both conditions by figs. 24 and 25 of his series, 

 the latter showing five and the former ten plates between the 

 dorsocentral and the radial primaries. Fig. 24, which I here 

 repeat (fig. n), was copied by myself for the purpose of 



Fig. II.— (' Quart. Journ. Micr. Sci.,' 1882, vol. xxii, p. 380.) Apical system 

 of the young Amphiura squamata; Stage III, after Ludwig. 

 1. Dorsocentral. 2. Under-basals. 3. Basals. 4. Radials. r. s. Ra- 

 dial shields. 



demonstrating that plates corresponding in position to the 

 under-basals of a Crinoid (2) were developed in the young 

 1 Loc. cit., p. 195. 



