ECHINODERMATA—CRINOIDEA. 



501 



radial extremely small. Tegmen somewhat extended posteriorly, 

 forming an elongate sac, the first plate of which closely resembles 

 the superradial in form and size. Arms simple, without pinnules. 

 Ordovicic. 



7. H. pristinus Billings. Ordovicic. 

 Closely similar to H. tumidus, but plates not so convex and more 



coarsely granular. 

 Chazy of Quebec. 



8. H. tumidus Billings. (Fig. 1812.) Ordovicic. 

 Plates tumid in the center, obscurely granular. 



Trenton of Ottawa. 



VI. Anomalocrtnus Meek and Worthen. 

 Calyx very large, subglobose. B 5. R irregular, that of the 

 posterior ray often longitudinally bisected in the median line. Ven- 



FlG. 1812. Hybocrinus tumidus. (Af- Fig. 1813. Anomalocrinus incurvus, 



ter Billings, Can. Org. Rem. Dec, IV.) posterior view ; an additional basal piece 



occurs. (After Meek, Pal. Ohio.) 



tral sac small and tubular. Arms uniserial and bifurcating. Pin- 

 nules given off in series alternately. Ordovicic. 



9. A. incurvus Meek and Worthen. (Fig. 181 3.) Ordovicic. 



Surface granular. 

 Cincinnatian of Ohio. 



VII. Heterocrinus Hall. 

 Calyx small, with long and cylindrical arms. Three of the R 

 compound, the others simple and shorter; the inferradial of the 



