INVERTEBRATE PAL2EONTOLOGY. 225 



small, rather depressed, located jusl behind the middle of the shell. Surface 

 marked by very fine lines of growth. 



Length, 1.56 inches; height, 1.05 inches: convexity, 0.56 inch. 



I have not vel seen the hinge or pallial impression of this species, and 

 consequently have some doubts in regard to its affinities, though an examina- 

 tion, of better specimens than those first obtained indicates that it is most 

 probably a Thracia. 



It appears to be related in form and other external characters to some 

 of the shells referred by Professor Agassiz to his genus Corymya, among 

 which we would mention the Liassic species G. lens (Etud. Crit. sur les 

 Moll. Foss., tab. 36, figs. 1-15). Our shell, however, has its beaks located 

 farther forward, and is proportionally more depressed and elongated than 

 young individuals of G. lens of the same size. 



M. d'Orbigny describes a few Cretaceous species in the Palaeontology of 

 France, resembling this more or less in form, which he refers to the genus 

 Periploma; they all differ, however, in having slightly more gibbous beaks, 

 and straighter ventral margins. 



Locality and position. — Same as last. 



T h r a c i a i Prouti, M. & H. . 



Plate 37, tigs. 6, «, b. 



Tellina Pruuti, Meek and Hayden (April, 1856), Proceed..Aea<l. Nat. Sci. Philad., VIII, 83. 

 Thracia Prouii, Meek and Hayden (18G0). ih., XII, 425; Meek (1864), Smithsonian Check-List, 14. 



Shell transversely ovate, compressed, very thin and fragile : right valve 

 slightly more convex than the left; anterior end elliptically rounded; poste- 

 rior half more contracted, and narrowly rounded or subtruncated at the extrem- 

 ity, provided with an obscure ridge extending from the beaks to the postero- 

 basal margin ; base, forming a broad semi-ovate Tiurve, more or less warped 

 or slightly curved laterally ; dorsum declining gradually with a convex out- 

 line in front of the beaks, concave immediately behind them, and sloping 

 posteriorly; beaks moderately elevated, closely approximate or touching, a 

 little iiibbous, located very near the middle of the shell; surface marked by 

 fine lines of growth. 



Length, 2A2 inches; height, 1.60 inches ; convexity 0.83 inch. 



The posterior muscular impression (I have not seen the other one) is 

 subtriangular, and placed between the postero-dorsal margin and the oblique 



lid II 



