94 CLEIOCRINUS. 



equivalent to the Middle Bala of England, and to Stage d 4 of Barrande's 

 section of the Ordovician of Bohemia. 



I have recently had the opportunity, thanks to the favor of Dr. J. F. 

 Whiteaves, to examine all the material of the genus belonging to the 

 Geological Survey of Canada, with results of such extraordinary interest 

 as to warrant a special account of it, in advance of the Memoir as to which 

 my investigations were more especially directed. 



HISTORY OF THE GENUS. 



Billings's account of the genus, as given in Decade IV., p. 52, is as 

 follows : — 



" Generic characters. — Cup, large, conical or pyriform ; basal plates, five; 

 rays, five, alternating with the basal plates; the third plate of each ray 

 is pentagonal and bears two secondary rays, which are several times 

 divided above. Between two of the rays a single vertical series of azygos 

 interradial plates extends from the base to the margin of the cup. The 

 azygos plates and rays are all firmly anchylosed together by their lateral 

 margins up to the height of the fifth or sixth sub-division. The column is 

 pentagonal or nearly round. 



"This genus has the structure of a Pentaerinus, with numerously divided 

 arms all soldered together in the walls of the cup." 



Von Zittel in 1879 * referred the genus to the family Crotalocrinidoa. 



In the same year Wachsmuth and Springer! referred it to the Ichthy- 

 ocrinidse, and discussed it as follows : — 



" The generic description was made from a single specimen, and this 

 was in several respects defective. Cleiocrinus has, according to Billings, 

 five basals alternating with the radials, and forming with them a belt 

 around the column. Such a structure has never been found in any Crinoid. 

 In the typical specimen, the comparatively large column conceals from view 

 the lower part of the calyx, a space large enough to accommodate one or 

 two series of plates, and analogy suggests that this may have been the 

 case. The five plates which Billings found alternating with the primary 

 radials. and which he called basals, are certainly interradials ; and as the 

 specimen in every visible character closely resembles IcHhyocrinus and 



* Eandb. der Pal., I., p. 357. 



f Revision of the Palseocrinoidea, Pt. I., pp. 35-36. 



