292 PROCEEDINGS OF THE ACADEMY OF [1885. 



frequently by muscles also, as seen by the articular faces of 

 Forbesiocrinus nobilis (PL 5, figs. 3 and 4), and we have seen 

 similar faces in Ichthyocrinus and Taxocrinus. Among the later 

 Poteriocrinidse there are also several genera with fossae along the 

 lateral faces of the radials, which indicate a certain degree of 

 mobility even among the plates of the calyx. On the other hand, 

 the higher radials of the Apiocrinidse, which Zittel refers to the 

 Articulata,are as solidly united among each other directly, or by 

 means of intercalated plates, as in an y so-called " tessellate " Cri- 

 noid. All of this tends to prove that a division based upon the 

 mode of union between the plates is totally impracticable, if 

 intended to separate the palaeozoic from the later Crinoids, as 

 done by Zittel. We think, however, it affords important data for 

 establishing subdivisions of the Palseocrinoidse, among which we 

 recognize Articulata and Camarata, the former having their plates 

 connected by articulation, the latter by suture. 



The distinctions between the Neocrinoidea and Palseocrinoidea, 

 according to Carpenter (Challenger Report, pp. 149-154), are 

 the following : — 



1. In the Neocrinoidea, underbasals are rarely represented ; in 

 the Palseocrinoidea, frequently. 



2. In the Neocrinoidea " by far the greater number of genera 

 have five equal and similar basals, with five equal and similar 

 radials resting upon them." Exceptions to this rule are found 

 in Hyocrinus, which has three basals, and JSolopus and Eudesi- 

 crinus in which the radials are not symmetrical ; " but this want 

 of symmetry is not due to the intercalation- of any anal plate as 

 in nearly all Palseocrinoids." 



3. In all Neocrinoidea, with the exception of Thaumatocrinus, 

 " the primary radials are in contact with one another by the 

 entire length of their sides ; or more rarely, as in Guettardi- 

 crinus, Uintacrinus and Apiocrinus roissyanus, their distal angles 

 are cut away so as to receive the lower part of the first inter- 

 radial. This feature, which is common enough in the Palseo- 

 crinoidea, is rare in the Neocrinoidea." 



4. Most of the Neocrinoidea have no interradial plates in the 

 calyx, but when present " they are not limited to any special 

 side of the calyx, but are equally distributed all round it, so that 

 there is no distinction of the anal side, Thaumatocrinus excepted." 

 In the Palseocrinoidea, however, "the pentamerous symmetry of 



