REPORT ON THE CRINOIDEA. 39 
plate. Hewxacrinus, Dichocrinus, and their allies present a similar condition. In a few 
genera of the Rhodocrinide, which have been grouped together into a section Rhodocrinites 
by Wachsmuth and Springer, the radials are not contiguous laterally; but between every 
two there is an interradial plate which rests on a basal below. 
This character, which occurs in no stalked Neocrinoid, either recent or fossil, reappears 
in the singular Comatulid Thawmatocrinus’ (Pl. LVI. figs. 1-4). But with this excep- 
tion all the primary radials of every adult Neocrinoid, recent or fossil, stalked or free, 
form a complete ring. 
Calyx-interradials are very usually present in the Palzocrinoids, helping, together with 
the higher orders of radials, to mcrease the size of the cup, and strengthen its walls. 
According to Wachsmuth and Springer? “The first interradial is always larger than 
any of the rest, and is situated between the upper sloping margins of the adjoining first 
radials, except in some species of the Rhodocrinide, in which it rests directly upon the 
basals, separating the ring completely. There are generally two plates in the second 
series, and two or three in each succeeding one.” 
In the Mesozoic genus Guettardicrinus, and in some species of Apiocrinus (Apioerinus 
martini, Apiocrinus roissyanus), there are calyx-interradials essentially similar to those 
of the Palocrinoids. Each series commences with a single plate resting upon the upper 
angles of two first radials which are truncated for its reception (see fig. 9, on p. 183). 
It is followed by several others, more or less irregularly arranged ; and these, together 
with the two outer radials, and sometimes also the two lower brachials, form the im- 
movable wall of a large cup just as in the Palocrinoids. No recent Crinoid presents 
this condition, at any rate in the adult state; though it occurs in many Ophiurids, as 
pointed out elsewhere.? But in all the Pentacrinide, recent and fossil,* the interradials, 
if present, are not calyx-plates at all, but merely small and more or less irregular 
plates developed in the perisome which unites the rays and their subdivisions (Pl. XIII. 
fig. 1; Pl. XXXI. fig. 2; Pl. XXXIV. fig. 1; Pl. XXXV. fig 7) "Pl ROR Tien t; 
Pl. L. fig. 1). It would seem, however, that regular calyx-interradials may appear in 
the early larval stages of Antedon rosacea. At any rate this is the way in which I 
should interpret the following statement by Sir Wyville Thomson.’ ‘In one or two 
cases, however, I have observed about the time of the first appearance of the anal plate, 
a series of five minute rounded plates developed interradially between the lower edges of 
the oral plates and the upper edges of the basals.” These plates therefore, separate 
the radials from one another all round the calyx. Their ultimate fate is uncertain. Sir 
1 On a new Crinoid from the Southern Sea, Phil. Trans., 1883, pp. 919-926, pl. 71. 
2 Revision, part ii. p. 12. 
3 On the Apical System of Ophiurids, Quart. Journ. Micr. Sci., vol. xxiv., N.S., January 1884, p. 12. 
4 See, for example, Quenstedt’s Encriniden, Tab. 101, figs. 23, 39a ; Austin’s Crinoidea, pl. xiii. fig. le; and 
Buckland’s Geology (Bridgewater Treatise), vol. ii., pl. lili. fig. 2. 
5 Phil. Trans., 1865, p. 540. 
