502 NORTH AMERICAN INDEX FOSSILS. 



posterior ray has the form of an axillary, supporting to the left 

 the ventral sac, and to the right the stiperradial. Arms compara- 

 tively stout, giving off long branchlets at intervals which often 

 branch again. Stem very large, five- 

 sided, divided by five partitions, the 

 lines of division being interradial in po- 

 sition. Ordovicic. 



10. H. simplex Hall. {H. canadensis 

 Billings.) (Fig. 1814.) Ordovicic. 



Pinnules directed upward nearly par- 

 allel with the rays. Column broadening 

 towards base of calyx. 



Cincinnatian of Ohio ; Trenton of On- 

 tario and Quebec. 



11. H. tenuis Billings. Ordovicic. 

 Much smaller and more slender than 



H. simplex (length, including arms, 

 about one inch). Column moniliform 

 to base of calyx. 



Trenton of Ontario and Quebec. 



VIII. Calceocrinus (Hall) Ringue- 

 berg. 



Calyx and arms bent down on the col- 

 Fig. 1814. Heterocrinus ^^j^n-so as to '' resemble a wilted flower," 



simplex; the larger is var. , . , . . , . , 



grandis, with enlargement of ^he right posterior intcrray lying along 

 arms. (After Meek.) the Stem. Calyx laterally compressed, 



being almost linear at the junction of 

 B and R. Anterior side flat, broadly truncate below, constricted 

 in the middle and composed of the R plates (the anterior and the 

 usually compound left and right anterior lateral R). B on the 

 posterior side, separated from the R of the opposite side by a 

 widely gaping articular line. Posterior side consists, in addition 

 to the B, of three plates, the left posterior and the compound right 

 posterior R. The right posterior and right anterior lateral super- 

 radials are fused into a T-shaped piece abutting with either wing 

 against the right posterior and right anterior lateral inferradials. 



