12 P. HERBERT CARPENTER. 



not separating them laterally as the anal plate does. These 

 plates reappear in a few Neocrinoids such as Gruettardi- 

 erinns and Apiocrinus roissyanus, where they form part 

 of the calyx just as in the Palaeocrinoids ; and their represen- 

 tatives are readily distinguishable in Ophioglypha minuta, 

 and Ophiomusium pulchellum (PI. 1, figs. 8, 9; i), as 

 in all those Ophiurids in which the large radial primaries meet 

 one another laterally and form a complete ring around the 

 dorsocentral. 



But in the recent Thaumatocrinus,^ as in the Palaeozoic 

 Rhodocrinus, Thylacocrinus, and other genera included 

 by Wachsmuth and Springer in the section Rhodocrinidae, 

 the primary interradial plates rest directly upon the basals and 

 completely separate the first radials from one another all round 

 the calyx ; and this indicates the persistence of an exceedingly 

 early developmental condition. A precisely similar arrange- 

 ment is presented by those Ophiurids in which the radial 

 primaries do not meet one another laterally, but are separated 

 by the proximal interbrachial plates, e.g. Ophioglypha 

 lapidaria (PI. I, fig. 4), Ophiomusium flabellum (fig. 3), 



0. granosum (fig. 7), and Ophiozona antillarum (fig. 

 6). These proximal interbrachials (i) rest directly upon the 

 basals (3), which are situated inside the circle of primaries (4). 



The radials of the Neocrinoid are primitively separate (PI. 



1, fig. 11 J 4) but ultimately approach one another and 

 form a closed ring (fig. 10) ; whereas in the Ophiurid they are 

 at first in close lateral contact both with one another and with 

 the dorsocentral (fig. 13). In some species (figs. 1 — 4, 6 — 8) 

 they subsequently become separated by the intercalation of 

 Ludwig's intermediary plates, i. e. the basals, under basals, and 

 the'proximal interbrachials, as shown by Ludwig's figures of 

 Amphiura (PL I, fig. 12). This separation of the radial 

 primaries in Ophiurids is readily explained by their want of 

 any relation to important internal organs, such as is charac- 

 teristic of the radials of a Crinoid, which protect more or less 



' " On a new Crinoid from the Southern Sea," * Proc. Roy. Soc.,' No. 225, 

 1883. 



