504 



NORTH AMERICAN INDEX FOSSILS. 



14. H. bradleyi Meek and Worthen. (Fig. 181 5.) Mississippic. 

 Column thick, composed of round plates which become some- 

 what pentagonal near the calyx; arms bifurcate frequently. 



Keokuk of Indiana. 



X. Carabocrinus BiUings. 



Closely similar to Cyathocrinus in form of calyx, mode of 

 branching, delicacy of arms, etc., but differs in the anal area which 

 here is composed of three plates, the lowest one resting on the IB. 



Trenton of Tennessee and Canada. 



15. C. geometricus Hudson. (Fig. 1816.) Ordovicic. 

 Small. Differs from C. radiatns in its less globular form. 

 Chazy of New York. 



16. C. radiatus Billings. (Fig. 1817.) Ordovicic. 

 Calyx globose, covered with rounded ridges. 



Trenton of Ottawa. 



XL Dendrocrinus Hall. 

 Calyx obconical, with height exceeding width. Structure of 

 calyx as in Cyathocrinus^ except that in Dendrocrinus the right 



Fig. 



Carabocrinus radiatus, opposite sides of different specimens. 

 (After Billings, Can. Org. Rem. Dec, IV.) 



posterior R is compound by a vertical division and the ventral sac 

 is very large, its base formed by the two or three plates which 

 succeed the IRA and which are partly enclosed in the calyx. 

 Ordovicic-Siluric ? 

 17. D. conjugans Billings. Ordovicic. 



Height and greatest width of calyx about one third of an inch. 

 Arms half the width of the R and rounded, twice bifurcating. 



Trenton of Ottawa. 



