MORPHOLOGICAL PART. 107 



integument was regarded as a structure sid generis, to which the term "vault" 

 was applied. The inner integument appears at first sight as if composed of 

 independent, ill-formed pieces ; but on closer inspection it is found that 

 these so-called plates are extensions from the plates above, and continuous 

 with them. Each lower part is connected with the corresponding upper one 

 by small surfaces or pillars, and joining by its edges with other like plates, 

 leaves open spaces or meshes along the sides. The inner portions constitute 

 a kind of internal lining or network, extending from the first costals and first 

 interbrachials uninterruptedly to the margins of the orals. In some speci- 

 mens only the pillars are preserved, the lateral extensions of the plates being 

 wanting ; while in others the floor is almost entirely smooth. The latter is 

 the case in Oadocrinus froloscidalis (Plate V. Fig. 10) ; while in Teleiocrmus 

 rudis (Plate V. Fig. 16), and in the specimen of Dorycrinus {ibid. Fig. 13), the 

 grooves are formed into well defined tunnels. A further indication that there 

 were probably two integuments in some of the Camerata at least, seemed 

 to be presented by the ventral structure of Siphonocriniis armosiis from the 

 Niagara group (Plate XIX. Figs. 3 a, h, c). This species, so well known from 

 natural casts, has a large, trumpet-shaped, subtegminal anal tube, which 

 crosses the mouth, overlies the upper ends of the ambulacral tubes, and is 

 continued subtegminally all the w^ay to the anterior side of the calyx, even 

 beyond the arm regions, where it bends outward. The case is best illus- 

 trated if we imagine the disk of a recent Crinoid, with an anal tube like 

 that of Antedon regalis (Chall. Rep. on the Comat., Plate XLYI. Fig. 2), 

 extended all the way out to the arm bases of the anterior ray, and covered 

 by a vault. 



It seemed hard to account for the facts presented by these cases, except by 

 the presence of two distinct structures covering the body cavity ; and upon 

 these specimens principally we formed the opinion, in the first instance, that 

 the Camerata had a vault and a subtegminal disk, and that the vault was 

 a structure without a parallel in recent Crinoids. The evidence appeared 

 to be conclusive that the disk was subtegminal, in some groups at least, and 

 this, which had been generally acknowledged by leading authors, led us to 

 believe that in all Camerata the disk was roofed over by a vault. In fact 

 this conclusion seemed to be corroborated by the nature of the plates, which, 

 although varying considerably in size and number, are arranged in all these 

 Crinoids on the same general principle, forming in all of them a compact, 

 rigid test, with the mouth and food grooves perfectly closed. 



