1881.] NATURAL SCIENCES OF PHILADELPHIA. 365 



3. RETEOCRINTJS Billings. 



1859. Billings. Geol. Rep, Canada, Decade iv, p. 63. 



Syn. Glyptocrinus (in part), Hall 1866 and 1872 ; Meek 1873. 



Among the species described by Hall under Glyptocrinus, there 

 is one — Gl. O^Nealli — which in several important characters differs 

 from his typical form. It has well-developed uuderbasals, ver}"^ 

 large basals, a pentagonal stem, and exceedingly depressed inter- 

 radial and anal regions, peculiar radial plates, etc., in all of which 

 characters it agrees with the genus Reteocrinus Billings, which was 

 described from imperfect material, and altogether misunderstood 

 by its founder. According to Billings, the calyx consists of a 

 reticulated skeleton, composed of incomplete or rudimentary plates, 

 each consisting of a central nucleus with three to five stout pro- 

 cesses radiating from it. Of such plates he describes three rings 

 of five each, corresponding in their position with the underbasals, 

 basals and first radials of other crinoids, and he compares the 

 genus with Cyalhocrinus, Dendrocrinus and similar forms. 



This description at first glance does not agree with Gl. 0''Nealli, 

 but a closer comparison with Reteocr. stellaris Billings shows at 

 once a remarkable similarity in the form and arrangement of these 

 rudimentary plates with the principal plates of the former species, 

 and leads to the conclusion that the interradial plates, which are 

 said to be wanting in Reteocrinus, really exist there, but are so 

 deeply imbedded within the depression as to be hidden from view 

 b}^ the matrix. Even in Glyptocr. (?) O^Nealli, the construction 

 of the interradial spaces is but rarely observed. Looking at the 

 specimens in the condition in which they are generally found, they 

 agree remarkably well with Billings' description. The second 

 and third primary radials appear to be free plates, and the calyx 

 seems to be composed of only three rings of plates like in the 

 Cyathocrinidse. 



The resemblance of Gl. O^Nealli with the genus Reteocrinus, 

 was pointed out already by Meek (Paleont. of Ohio, i, p. 34), but 

 he left the species under Glyptocrinus ; also Wetherby noticed 

 this similarity in the description of his Glyptocr. Richardsoni, 

 and he agrees with us, that both his species and Gl. 0''Nealli 

 should be arranged under Reteocrinus. 



A reconstruction of the genus with Gl. O^Nealli = Reteocr. 

 iVNeoMi, as t^pe, will, we believe, clear up a number of difficulties, 

 and we accordingly propose the following : — 



