146 Annals of the Carnegie Museum. 



Cf. Loxoptei-ja (/is/>ar Clarke, 1903. " The Naples Fauna in Western New York; 

 Memoir of N'e7v York State JMuseuni,'" No. 6, p. 272, PI. 13, figs. 8-17. 



Description. — Shell somewhat triangular in outline, insequivalve, 

 the right valve nearly flat, the left valve capuliform. 



The right valve is slightly convex, sometimes quite flat. A narrow 

 sulcus extends from the beak to a notch in the posterior margin of the 

 shell, and delimits a wing-like portion of the valve. There is no pos- 

 terior gape observable in any of the shells in the collection, but the 

 thin margins of the " ears " are frequently broken. 



The left valve is strongly elevated and acute in the umbonal region, 

 but the beak is incurved almost to the hinge. The anterior end of the 

 valve is smoothly rounded, the length of the hinge being less than the 

 length of the shell. From the highest point on the valve to the ante- 

 rior margin the slope is gradual, but the posterior slope is abrupt and 

 slightly concave. This concavity is broken by a ridge which extends 

 from the posterior side of the beak to a rounded, ear-like extension of 

 the posterior margin of the valve. 



The surface of both valves is marked by numerous fine, radiating 

 striae. The right valve also shows a few rather strong concentric undu- 

 lations. 



No muscle scars have been observed on the left valves, but some of 

 the better preserved casts of the interiors of right valves show a small 

 but strong oval posterior scar and an apparently entire pallial line. An 

 anterior muscle was undoubtedly present, but its scar has not been de- 

 tected on any of the specimens at hand. 



The prodissoconch is retained on both valves, and is set off from 

 the remainder of the beak by a shallow groove. Its position shows a 

 clock-wise tortion of the shell during growth. 



The ligament was external. The ligamental area on the left valve 

 is triangular, with the apex of the triangle directly beneath the beak. 

 On the right valve the greater part of the ligamental area is posterior 

 to the beak, and its plane is at an angle of about 45 ° to the remain- 

 der of the valve. No striations were observed on the ligamental area. 



This species seems closely allied to Loxopteria dispar (Sandberger), - 

 as described by Freeh, but differs from that species in having the wing 

 of the right valve more sharply defined and in the ornamentation of 

 the same valve by strong concentric undulations. 



From Loxopteria dispar d& described by Clarke from specimens ob- 

 tained in western New York, our specimens difi'er in having a small 



