380 



p. HERBERl' CARPENTER. 



According to Ludwig, this inner ring has been seen in Amphi- 

 ura sqt(,a7nata and in other species (though not understood) by 

 Schultze, Krohn, Agassiz, and Metschnikoff. He speaks of 

 the plates as primary radials, from which I infer that he regards 

 them as representing the radials of a Crinoid (fig. in, 4), and 

 the ocular plates of an Urchin, though he never expressly says 

 so. Together with the dorsocentral they form the rosette of six 

 primary plates, which is a prominent feature on the abactinal 

 surface of many adult Ophiurids. In AmpUura squamaia, hovy- 

 ever, they become separated by the appearance of two rings of 

 intermediate plates between them and the dorsocentral. The 

 plates in the outer ring (fig. ii, 3) are interradial, while those of 



Tig. II. — Apical system of a slightly older Amphinra, in which the Termi- 

 nalia have been carried out to the ends of the rudimentary arms, and 

 llie orals have passed over on to the ventral side. 1 and 4 as in Fig. I, 

 after Ludwig. 2. Proximal row of intermediate plates representing 

 the under-basals of a dicyclic Crinoid. 3. Second row of intermediate 

 plates representing the basals of a Crinoid. Outside each of these 

 are two other interradial plates, r.s. Radial shields. 



the inner ring next the dorsocentral are radial in position (fig. 

 II, 2) . In these plates we have, I believe, the representatives of 

 the dicyclic base of Marsupites and other Crinoids, viz. a proxi- 

 mal ring of under-basals hitherto unknown in any of the Echi- 

 nozoa, and a distal ring of interradial plates ^ corresponding to 



' These must not be confounded with the interradial plates seen by 

 Agassiz in Ophioplwlis bellis, and compared by him to the interradial plates 

 of an Asterid (' Embryology of Echinoderms,' p. 18, fig. 29). The former. 



