FOSSILS OF THE POTSDAM GROUP. 



^ 



BEACHIOPODA. 



Genus OBOLELLA Bill. 

 Obolella discoid a n. sp. 



Plate I, figs. 1-2. 



Shell very small, discoid, and scale-like; valves depressed convex; the 

 larger one a little longer than wide, giving a very short, ovate form, only 

 perceptibly narrowing toward the beak, rounded on the sides and a little 

 straightened on the front margin; surface slightly convex, more convex on 

 the umbo and flattened toward the front. Smaller valve circular, sometimes 

 almost truncate at the beak, slightly convex on the umbo, and flattened in 

 front, having a less degree of convexity throughout than the other valve. 



Surface-structure not observed. The shells are all more or less exfo- 

 liated by separation from the rock. The substance of the shell is calcareous, 

 and the surface of the cast smooth and shining, with very fine concentric 

 lines. 



The shells seldom measure more than an eighth of an inch in their 

 greatest diameter, and are usually smaller; while the largest examples seen 

 do not exceed one-sixth of an inch. It is remarable only for its small size 

 and flattened form, possessing no salient features by which it can be com- 

 pared with other species. 



Formation and locality. — Quite common in some hard, sandy limestones 

 of the Potsdam formation, in the Eureka District, Nevada, associated with 

 Kutorgina, Agnostus, and several species of Trilobites. Collected by Arnold 

 Hague, esq. 



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