170 PALEONTOLOGY OF THE EUKEKA DIS1EICT. 



Valves with small incurved beaks situated well towards the anterior 

 end of the nearly straight cardinal line. 



Surface, as shown by the impression left in the cast, marked by con- 

 centric lines of growth. 



Dimensions: height, 4 cm ; breadth, 6. 5 cm ; convexity of right valve, 17 mm . 



Four specimens of this species have been obtained, all in the form of 

 casts. The transverse subquadrangular form serves to distinguish it from 

 Modiomorpha alia of the Hamilton Group of New York, which is the most 

 nearl}^ allied species. Some specimens that are referred to M. alia are 

 almost identical in form, but the typical forms differ materially, as may be 

 seen by comparing our figure with those given of the New York species 

 (Pal. N. Y., vol. v, pt. 1, Plates and Explanations, pi. xxxvii). 



Formation and locality. Lower Devonian ; Lone Mountain, 1 8 miles 

 northwest of Eureka, Nevada. 



Modiomorpha oblonga, n. sp. 

 Plate v, fig. 7. 



Shell transversely elliptical or elongate-ovate. General surface mod- 

 erately convex, with a distinct, rounded umbonal ridge. 



Hinge-line shorter than the length of the shell and nearly straight. 

 Beaks anterior, small, and incurved. Surface marked by concentric lines 

 of growth. 



Dimensions: height, 2.75 cna ; breadth, 5.5 cm ; convexity of left valve, 

 0.75^. 



This species is more nearly related to Sanguinolites ? Sanduskyensis Meek 

 (Pal. Ohio, vol 1, p. 209, pi. xviii, fig. 3), from the Helderberg Group of 

 Ohio, than to any other species with which we are acquainted. It is less 

 expanded posteriorly, and the anterior extremity is not as uasute. The 

 generic reference is made on the general form, as the hinge characters are 

 unknown. 



Formation and locality. Lower Devonian of Atrypa Peak, Eureka 

 District, Nevada. 



