h^y'i 







4 P. HERBERT CARPENTER. 



under-basals of ^Crinoids.^ The uniformity in the composition 

 of the apical system or calyx in all the three groups of 

 brachiate Echinoderms thus becomes exceedingly striking. 



It will be remembered that I have pointed out the presence 

 of under-basals in the young Amphiura squamata^ (PL I, 

 fig. 12 ; 2). Since then I have searched through all the figures 

 of the disc in adult Ophiurids which I could find, especially 

 those in Lyman's admirable memoirs; and I have been sur- 

 prised to discover in what a number of species the homologues 

 of the plates of the Crinoidal calyx may be detected in the 

 rosette which occupies the centre of the disc. 



Lyman ^ describes this rosette as made up of " primary 

 plates which lie on the back of the disk, one in the centre, and 

 ten others radiating from it; they may be distinguished by 

 their greater size. In the young animal they cover the whole 

 back of the disc and are only six in number." He describes 

 these six elsewhere,* as arranged with " the largest in the 

 centre and the other five in a close circle round it, one opposite 

 the base of each arm,^' i.e. the " primary " plates of the young 

 Ophiurid are radial in position. This is well shown in the 

 larval Amphiura squamata described by Ludwig. A dia- 

 gram based upon one of his figures appeared in my fifth note 

 and is reproduced in PI. I, fig. 13. The same point is also 

 well illustrated by two figures of the young Hemipholis 

 cordifera given by Lyman.5 At a later stage of development 

 one or even two rings of plates come to intervene between 

 these primary radials (4) and the dorsocentral (1), as shown 

 in PI. I, fig. 12. They represent the basals, and occasion- 

 ally also the under-basals, of a Crinoid, as I have already 

 pointed out ; and the former sometimes retain a considerable 

 relative size in the adult form (PI. I, figs. 3, 4, 5, 7; 3). 

 In some species, too, the large '' primary " plates which 



- ^ * Trans. Roy. Soc.,' Edinb., vol. xxxii, p. 

 « Note v. Tbis Journ., vol. xxii, p. 3S0. 



3 '* Opliiuridae and Astfophytidse," 'Mem. Mus. Comp. Zo6l,'vol. i, No. 3. 

 * " OphiuridK and Astrophjtidae, New and Old," ' Bull. Mus. Comp. Z06I.,' 

 vol. iii. No. 10, p. 26i. 

 » 'Report on the "Challenger" Ophiuroidea,' p. 157, PI. xl, figs. 11, 12. 



