516 Systejiatic Paleontology 



in front. Hinge straight, long, about four-fifths the greatest length of 

 the valve. Ventral outline gently convex at the extremities, curving up- 

 vrard more rapidly behind than in front. Post-marginal part of valves 

 marked by a low swelling which merges into a much fainter rim along the 

 ventral edge, and is lacking in the posterior half. This rim becomes quite 

 obsolete anteriorly. Within the anterior edge and about the midheight 

 of the valve is a prominent, though compressed, ridge-like node. Sulcus 

 strong and deep, subcentral and occupying the dorsal half of the valve, 

 with broad though not sharply defined swellings on each side. 



Length .72 mm. ; height .40 mm. 



None of the described American species of Primitia are close enough to 

 P. postturgida to require comparison, but P. divisa Jones and Holl, from 

 the Wenlock of England, is somewhat similar in shape and surface mark- 

 ings. In the latter species, the sulcus and the lobes surrounding it are not 

 as well marked, in fact, the posterior lobe is almost wanting, while the 

 place of the anterior is occupied by a small node. The swollen area en- 

 closing the sulcus is somewhat suggestive of the horse-shoe shaped ridge 

 of species of Bollia like B. ungula and B. curta, figured on the same plate. 

 This possible alliance is further indicated by the marginal thickenings 

 described. 



Occurrence. — Oriskany Formatiok, Shriver Member. 21st Bridge. 



ColJection. — U. S. N"ational Museum. 



Prijiitia ? cumberlandica n. sp. 



Plate XCV, Fig. 5 



Description. — Carapace obliquely subovate, widest in the middle third, 

 with a straight hinge-line nearly as long as the greatest length of the valve. 

 Post-dorsal angle obtuse, antero-dorsal angle sharper; ventral border 

 gently convex but turning upward more gradually in front than behind, 

 thus causing the anterior end to be narrower than the posterior. Free 

 edge of valve with a narrow, well-defined, and slightly raised border. 

 Sulcus short, straight, almost twice as long as wide, deep and well marked, 

 occupying approximately the central portion and not extending to the 



