8 PROCEEDINGS OF THE NATIONAL MUSEUM vol.78 



No species recorded from the interior province is sufficiently close 

 to Perlplomya? aspenana to deserve comparison. P. applicata^ from 

 the later Upper Cretaceous of the Coastal Plain, tapers more pos- 

 teriorly and has finer sculpture but is very similar in gross form. 



E olotype.— C^i. No. 73765, U.S.N.M. 



Family THRACIIDAE Dall 

 Genus THRACIA Leach 



THRACIA? WYOMINGENSIS. new species 



Plate 1, Figure 10 



Two natural casts of the exterior of right valves have the form of 

 some shells generally assigned to Thracia^ except that as here pre- 

 served they are not as inflated. Few details are preserved, but the 

 writers have ventured to apply a specific name in the belief that the 

 species will be recognizable in future collections. The specimens are 

 compressed, ovate in general outline, rostrate posteriorly; beak not 

 prominent, subcentral, with a diagonal depression extending pos- 

 teriorly from it. Anterior and basal margins evenly convex; pos- 

 terior margin nearly straight, vertical ; dorsal margin nearly straight 

 anteriorly, emarginate posteriorly, angle at the beaks 90°. Only 

 sculpture showm is distant concentric lines. Internal characters 

 entirely unknown. 



Length, 21 millimeters ; height, 18 millimeters ; depth, as preserved, 

 2 millimeters. 



No described form in the American Cretaceous known to the 

 writers is much like Thracia? luy owning ensis. 



H olotype.— Csit. No. 73766, U.S.N.M. 



Family TANCREDIIDAE Fischer 

 Genus TANCREDIA Lycett 



TANCREDIA? LINGO LNIANA, new species 



Plate 1, Figure 6 



A single mold of the exterior represents a left valve with the form 

 of some species of the genus Tancredia. It is compressed ; the dorsal 

 margin nearly horizontal for a distance of about 6 millimeters be- 

 hind the beak, very slightly emarginate in front of the beak, angle 

 at the beak about 150°; ventral margin gently and evenly convex; 

 the anterior margin tapered, the posterior rather sharply truncated 

 in an oblique direction and apparently permitting a gape. Beak in- 

 conspicuous; two faint depressions, possibly accidental, diverging 



