

PAL.-EOCRIXOIDEA. 4 2 5 



composed of the fragmentary remains of these organisms that they 

 may be properly spoken of as " crinoidal limestones " and " en- 

 crinital marbles." The Permian formation (Dyas) is singularly poor 

 in remains of Crinoids, and the commencement of Mesozoic time 

 appears to have been signalised by the complete disappearance of 

 the Palaeocrinoids, and the coming in of the Neocrinoids. The first 

 forms of this latter group make their appearance in the Trias (Encrinus, 

 &c), and numerous types are known in the Jurassic and Cretaceous 

 rocks, but the Crinoids no longer play a part of such conspicuous 

 importance as we have seen to have been the case in the Palaeozoic 

 period. The earliest forms of the great modern family of the Com- 

 atulidce appear in the lower part of the Jurassic system (Middle Lias). 

 The Tertiary formations are by no means rich in Crinoids, and the 

 comparatively limited recent Crinoidal fauna must be regarded as a 

 survival from the earlier part of the Mesozoic period, most of the 

 living types being closely connected with forms which existed at the 

 time when the Triassic and Jurassic deposits were laid down. 



In the following synopsis of the families of the Crinoidea, the char- 

 acters and distribution in time of the leading groups will be briefly 

 touched upon, but the less important families can only be defined 

 in the shortest manner possible. The arrangement followed is, in 

 the main, that adopted by Wachsmuth and Springer as regards the 

 Palaaocrinoids and by Dr P. Herbert Carpenter as regards the Neo- 

 crinoids. 



Division A. Pal^ocrinoidea. 



The division of the Palceocrinoidea corresponds with Miiller's 

 division of the Tessellata, as redefined by Zittel, minus the two Meso- 

 zoic genera Marsupites and Uintacrinus. The calyx in the Palaeo- 

 crinoids is comparatively large, with massive plates, and is usually 

 unsymmetrical, the arms being proportionately small. Interradials 

 are usually present, while the anal interradius is specially developed 

 and is readily recognisable. A certain number of the plates above 

 the primary radials are, as a rule, " closely united to one another and 

 to the interradials, so as to form the walls of a relatively large and 

 substantial calyx " (P. H. Carpenter). The ventral surface is covered 

 by a more or less extensive vault, the centre of which is generally 

 occupied by the united oral plates, concealing the mouth and the 

 origins of the ambulacra (fig. 297). 



Family 1. Acti?iocri?iid<z. — The calyx in this family is always 

 " monocyclic," there being three to five basals, but no " under- 

 basals" (fig. 299). The plates of the cup are firmly united by 

 suture, and the radials take part in the formation of the calyx. In- 

 terradial plates are developed, and the lowest " anal " interradial 

 rests directly upon the basals. The arms may be uniserial or biserial 



