REPORT ON THE CRINOIDEA. 149 
constitute a parallel group to the Palocrinoids, as Urchins are abundant in the 
Secondary and Tertiary rocks and also at the present time. But the Blastoids and 
Cystids shared the fate of the Trilobites, and did not persist into the Triassic Seas. 
Tt will now be advisable to discuss the various characters which distinguish the 
Neocrinoids from the Palzeocrinoids. Some of them have been alluded to elsewhere, but 
no attempt has yet been made to group them together. 
In the first place the calyx of a Neocrinoid is very symmetrical in its composition, 
though it may undergo more or less distortion, as in the Eugeniacrinidee and Holopide 
(Pls. I.-IV.). 
Under-basals are rarely present (Encrinus, Extracrinus, and Marsupites) ; while by 
far the greater number of genera have five equal and similar basals, with five equal and 
smilar radials resting upon them. HHyocrinus it is true has only three basals (Pl. VI.) ; 
while the radials of Holopus (Pl. III. fig. 1) and Hudesicrinus are not symmetrical ; but 
their want of symmetry is not due to the intercalation of any anal plate as in nearly all 
Palzeocrinoids, so that one side of the calyx becomes especially distinguished as the anal 
side. In all Neocrinoids, with the single exception of Thawmatocrinus, these primary 
radials are in contact with one another by the entire length of their sides; or more 
rarely, as in Guettardicrinus, Uintacrinus, and Apiocrinus,roissyanus,' their distal angles 
are cut away, so as toreceive the lower part of the first interradial. This feature, which 
is common enough in the Paleocrinoids, is rare in the Neocrinoids ; for the second radials 
are usually wider than the first, and more or less completely united to their fellows by 
their lower angles (Pl. XV. figs. 1, 2; Pl. XXIX. fig. 1; Pl. XXXVII. figs. 1, 2; 
ly SO OONN a fist LPL XLII, fies. 25.0 P lL XLIX. figs, 2), 
In like manner there is only one known genus and species of Neocrinoids 
(Thaumatocrinus renovatus, Pl. LVI. figs. 1-4) which has the rays completely separated 
by primary interradials that rest on the basals; though there are several genera of 
Palxocrinoids distinguished by this peculiarity, which is characteristic of the large and 
important family Rhodoerinidee (Wachsmuth and Springer). 
In most Paleocrinoids a certain number of the plates above the primary radials 
become closely united to one another and to the interradials so as to form the walls of a 
relatively large and substantial calyx. This is especially-the case in the Actinocrinide ; 
“while in the Platycrinide comparatively few plates are enclosed within the calyx, many 
of them, which in the Actinocrinidee form a conspicuous part of the body, being here 
found in the lateral appendages. In the Platycrinide the calyx proper is constructed 
almost exclusively of basals and first radials, all higher orders of radials either forming a 
part of the brachial appendages, or, when partially incorporated with the calyx, being 
insignificant compared with the other parts.” * 
In the Ichthyocrinidee, however, while the secondary and tertiary radials form a part 
1 See woodcut, fig. 9 on p. 183. ? Wachsmuth, Revision, part ii. p. 55. 
