CLEIOCRINUS. 



The genus Cleiocrinns was established by the eminent Canadian palaeon- 

 tologist, E. Billings, in 1856,* to receive certain very peculiar Crinoids 

 found in the Trenton Group of the Lower Silurian, at Ottawa, Canada. 

 It was based upon one species, C. regius, which he described at the same 

 time (he. cit., p. 277). In 1859 he published,! along with the generic 

 diagnosis, a full description, with good figures, of C. regius, the only species 

 in which the calyx was then known, and named two other species, C. 

 grandis and C. magnificus, upon fragments of the column ; — the main 

 apparent distinction of these being their larger size, and in C. magnificus 

 the less relative thickness of the column joints. 



The genus has been a puzzle to Crinologists ever since, — both as to 

 its actual structure and its systematic position. Its lowest ring of plates, 

 described by Billings as resting on the column, consisted of ten plates, — 

 five radially situate and five interradially, — which was so fundamentally 

 different from the calyx plan of all other known Crinoids that it was 

 impossible to assign a place for it without introducing hypothetical plates 

 within the proximal ring of Billings, concealed by the column. Inter- 

 pretations of the calyx based upon theories of this kind were none of them 

 satisfactory, and left the position and relations of the genus in much 

 doubt: 



The stratigraphic position of Cleiocrinns renders it a form of special 

 interest, because it is one of the earliest of known Crinoids. It is asso- 

 ciated with Blasioidoerinus, Palceocrinus, Hyboerinus, Carabocrinus, and other 

 primitive forms, in an epoch when the Cystids were the prevailing Echi- 

 noderm type. The Trenton Limestone is one of the oldest formations in 

 which Crinoids have been found. It is considered to be approximately 



* Report Geological Survey of Canada, 1856, p. 276. 



f Figures and Descriptions of Canadian Organic Remains, Dec. IV., pp. 52-5-1. PI. V. 



