FOSSILS OF THE LOWER SILURIAN. 



67 



of the great vertical difference in the geologic horizon at which the two 

 forms occur, render the probability of a specific identity very doubtful. 



Formation and localities. Upper portion of the Pogonip Group, White 

 Mountain and Goodwin Canon, Eureka District, Nevada. Also in the col- 

 lection of the School of Mines, Columbia College, New York, collected by 

 Dr. J. S. Newberry in the Pahranagat Range, Nevada. 



Receptaculites ellipticus, n. sp. 

 Plate xi, fig. 12. 



This is an elongate, flattened, curved form, with a strongly elliptical 

 transverse section, the curvature being with the major diameter of the 

 section. The central depression is deep, but not as large proportionally as 

 in R. elongatus. The plates of the ectorhin are of medium size, 1.75 mm by 

 1.25 mm , and arranged as in the preceding species. The cylindrical tubes 

 uniting the ectorhin and endorhin are strong and appear to be round and 

 smooth, except where marked by the constriction and connecting basal 

 stolons. The plates of the endorhin are concealed by the adhering matrix 

 in all the examples in the collection. 



The illustration shows the curvature and general form of a well-marked 

 example of the species. It is specifically distinct from any described form 

 that we know of, although allied to Receptaculites infundibulus Hall (Rep, 

 Geol. Surv. Wisconsin, 8vo, pam., p. 16, 1861) Ischadites tessellatus Win- 

 chell and Marcy, of the Niagara Group of Illinois (Mem. Bos. Soc. Nat. Hist., 

 vol. i, p. 85, pi. ii, fig. 3, 1865), from which it differs in the size of the 

 ectorhinal plates and other details of structure. 



Formation and localities. Upper portion of the Pogonip Group, White 

 Mountain, Goodwin Canon, and Fish Creek Mountains, Eureka District, 

 Nevada. 



BRACHIOPODA. 



Genus OBOLELLA Billings. 



Obolella ? ambigua, u. sp. 

 Plate i, fig. 2 a, b, c. 



Shell of medium size for the genus as now known, ovate, moderately 

 convex; surface lamellose; shell calcareous. Ventral valve ovate, broadly 



