48 CANADIAN FOSSILS. 



Genus Heteroceinus, Hall. 



(Hbteboceikus, Hall, Paleeontology of New York, volume i., page 2t8.) 



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Pig. 16. 



Figure 16. Diagram of the structure of the genus Heterocrinus, 



Generic characters. — The species of this genus are small, and, 

 including the arms, long and nearly cylindrical crinoids. The base 

 is composed of five plates, above which are five long rays, without 

 any intervening sub-radial plates. The number of radial plates in 

 each ray is variable. The cup appears to consist of the primary 

 radials, while the free rays or arms commence with the first plates 

 of the secondary rays. There are one or two small azygos inter- 

 radials, but no regular inter-radials. The arms are pinnulated. 



Heteroceinus Canadensis, Billings. 

 Plate IV. Figs. 5a-5d. 



(Compare JET. simplex, Hall, Paleontology of New York, volume i., page 280.) 



Description. — Sub-cylindrical or elongated, fusiform ; length, inclu- 

 ding the rays, from one to two inches ; diameter at half the length, 

 from three to four lines. The base in the large specimens is about 

 one line and a half in diameter, and the body gradually enlarges to 

 about three lines at that point where the rays divide. The diameter 

 above is always greater, the extent depending upon the amount of 

 expansion of the rays in the particular specimen examined. The 

 basal plates are scarcely a line in height ; the length of the undivi- 

 ded portions of the rays in the large individuals is about three lines. 



