REPORT ON THE CRINOIDEA. 149 



constitute a parallel group to tlie Palaeocrinoids, 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. 



It "ftall now be advisable to discuss the various characters which distinguish the 

 Neocrinoids from the Pateocrinoids. 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 Eugeniacrinidse and Holopidse 

 (Pis. I. -IV.). 



Under-basals are rarely present {Encrimis, Extracrinus, and Marsupites) ; while by 

 far the greater number of genera have five equal and similar basals, with five equal and 

 similar radials resting upon them. Hyocrinus it is true has only three basals (PI. VI.) ; 

 while the radials of Holopus (PI. III. fig. l) and Eudesicrinus are not symmetrical ; Ijut 

 their want of symmetry is not due to the intercalation of any anal plate as in nearly all 

 Pala)Ocrinoids, so that one side of the calyx becomes especially distinguished as the anal 

 side. In all Neocrinoids, with the single exception of TJiaumatocrinus, these primary 

 radials are in contact with one another l:)y the entire length of their sides ; or more 

 rarely, as in Guettardicrinus, Uintacrinus, and Ajyiocrinus^roissyamis,^ their distal angles 

 are cut away, so as toreceive the lower part of the first interradial. This feature, which 

 is common enough in the Palaeocrinoids, 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 (PI. XV. figs. 1, 2 ; PL XXIX. fig. 1 ; PL XXXVII. figs. 1,2; 

 PL XXXIX. fig. 1 ; PL XLIII. fig. 2 ; PL XLIX. figs. 1, 2). 



In like manner there is only one known genus and species of Neocrinoids 

 {Thcmmatocrinus 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 

 Palaeocrinoids distinguished by this peculiarity, which is characteristic of the large and 

 important family Ehodoerinidse (Wachsmuth and Springer). 



. In most Palaeocrinoids a certain numljer 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 Actinocrinidas ; 

 "while in the Platycrinidee comparatively few plates are enclosed within the calyx, many 

 of them, which in the Actiuocrinidse form a conspicuous part of the body, being here 

 found in the lateral appendages. In the Platycrinidae 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 lehthyocrinidse, however, while the secondary and tertiary radials form a part 

 1 See woodcut, fig. 9 on p. 183. " Wachsmuth, Eevision, part ii. p. 55. 



