CR USTA CEA—MALA COSTRA CA. 375 



7. R. ventricosa Whitfield. Ordoviclc. 



Small (less than three fourths of an inch long), strongly ventri- 

 cose; venter rounded; dorsum sloping; in internal mold is a strong 

 tubercle on each side of beak; differs from R. calcifera in being 

 more gibbous and less elongate behind, with more prominent 

 beaks. 



Beekmantownian (Fort Cassin) of Vermont. 



III. Ceratiocaris M'Coy. 

 Carapace consisting of a smooth, pod-shaped, bivalve shell, with- 

 out eye nodes. Valves of carapace elongate, subovate, or sub- 

 quadrate, narrow in front, truncated (but not incurved) behind. 

 A free lanceolate rostrum occurs. Body of 14 or more segments, 

 of which from four to seven extend beyond the carapace; some of 



Fig. 1676, Ceratiocaris acuminata, X 3^> showing one of the lateral spines. 

 (After Grabau.) 



these have obscure branchial appendages. Telson a long-pointed 

 spine, with two smaller lateral spines {cercopods) articulated to it. 

 Ordovicic-Siluric. 



8. C. acuminata Hall. (Fig. 1676.) Siluric. 

 Carapace large, tapering in front, broad medially, and rather 



abruptly truncated behind. Surface with fine, raised, longitudinal 

 lines. The next to the last segment long. Telson and lateral spines 

 short. 



Waterlime beds (Bertie) of North Buffalo, New York. 



IV. NoTHozoE Barrande. 

 Carapace of elongate to subquadrangular or nearly circular 

 \alves; both ends and ventral margin rounded, the dorsal margin 

 straight or gently curved; surface smooth. Cambric. 



9. N. vermontana Whitfield. (Fig. 1677.) Cambric. 

 Nearly circular; hinge line straight, less than greatest width of 



shell; sides and base rounded; surface smooth. 



Vermont quartzite (Lower Cambric or Georgian) of Vermont. 



