158 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



proportionaUj larger wings, narrower body, and a more nearly erect 

 axis. 



Position and locality. — ^Lower Potato Valley, Southern Utali, where it 

 was obtained by Prof. J. W. Powell from Cretaceous strata. 



Genus SOLEMYA Lamarck. 



SOLEMYA BILIX (sp. nOV.). 



Shell about two and a half times as long as high, broader anteriorly 

 than posteriorly ; both ends rounded, the posterior one more narrowly 

 so than the other ; both dorsal and basal margins gently convex or nearly 

 straight; test thin and fragile; valves moderately convex from above 

 downward, the greatest convexity in that direction being near the dor- 

 sum ; beaks, having the usual inconspicuous character common to the 

 genus, situated near the posterior end; ligament necessarily short, but 

 apparently well developed, and resting upou a fulcrum of support of the 

 usual character in each A^alve. Surface bright and, besides the usual 

 lines of growth, marked by numerous faint radiating lines, which are 

 visible to the unassisted eye, but are satisfactorily seen only under a 

 lens, nearly uniformly distributed over the whole surface, but ujion the 

 middle portion they are arranged in pairs. 



Length, 20 millimeters ; height at the broadest part, which is in front 

 of the middle, 8 millimetres. (Museum Xo. 8913.) 



This is plainly a characteristic species of Solemya, but the only fossil 

 species with which it need be compared is S. suhplicata Meek & Hay- 

 den, from the Fox Hills Cretaceous of the Upper Missouri. It differs 

 from that species in being proportionall}^ broader in front, in the charac- 

 ter and uniformity of distribution of its radiating striae, and in wanting 

 the subplicate character of the front portion. The extension of the epi- 

 dermis has not been observed, but in other respects this s]iecies may be 

 compared with the living S. velum Say in general form, and in the pair- 

 ing of its radiating lines. 



Position and locality. — Cretaceous strata, associated with Mactra holmesii 

 {=Gyrenaf holmesii Meek), about four miles north of Golden, Colo., 

 where it was obtained by Mr. W. H. Holmes. These strata were for- 

 merly supposed to belong to the Lignite series (Laramie), but they are 

 marine Cretaceous, as I have shown in An. Eep. U. S. Geol. Sur. Terr, 

 for 1877, pp. 193-196. 



Genus LUCINA Brugui^-e. 



LUCINA PEOFUNDA (sp. nOV.). 



Shell subcircular or subpentahedral ; valves not very convex ; pos- 

 terior side truncate, narrower than the anterior; basal border having its 

 margin more abruptly convex at its middle than towards the front and 

 rear; dorsal margin short, nearly straight; front margin having a nearly 



