STANTON.] 



CYRENID.E. 103 



but the cast of the same specimen would be much more nearly equilat- 

 eral. The surface is smooth with obscure lines of growth. The details 

 of the hinge are almost precisely the same as in the preceding species, 

 excepting that the anterior lateral tooth is much smaller. In form the 

 species is closely related to C. infiexa Meek. 



Locality and position. — From the coal-bearing sandstones at Bear 

 River city, Wyoming, probably near the top of the Colorado formation. 



Gyrena inflexa Meek. 



PL xxii. Fig. 13. 



Corbicula (Veloritina) inflexa Meek, 1873, Ann. Rept. U. S. Geol. Sur. Terr, for 1872, 



p, 493. 

 Cyrena inflexa White, 1879, idem for 1877, p. 290, PI. 10, Fi<>\s. la and b. 



Original description : 



"Shell longitudinally ovate, a little less than two-thirds as high as 

 long, moderately convex; posterior extremity rather narrowly rounded 

 or apparently sometimes faintly subtruncated ; anterior very short, sub- 

 truncated, or more or less sinuous in outline just in advance of the beaks 

 on the abrupt forward slope above, and rather abruptly rounded below; 

 basal margin semiovate or semielliptic; dorsal margins inflected and 

 forming a long convex slope from the umbonal region posteriorly ; beaks 

 rather depressed, oblique, incurved, and placed near the anterior end; 

 umbonal slopes not prominently rounded; surface merely showing fine, 

 rather obscure marks of growth ; anterior muscular impression rather 

 strongly defined and obliquely ovate; posterior muscular impression 

 larger and obscure; pallial line showing a deep, angular, ascending 

 sinus; posterior lateral teeth of hinge very long, linear, and nearly or 

 quite smooth; anterior short; cardinal teeth very oblique. 



" Length of a specimen, a little under medium size, 1.35 inches ; height, 

 0.39 inch; convexity, 0.68 inch. 



"This species is more depressed and elongated than any of those hith- 

 erto described from the far western localities, excepting one or two from 

 the coal formations on Bitter creek, Wyoming, from which it differs in 

 having its beaks placed farther forward. It will also be readily dis- 

 tinguished from those shells, as well as from all of the other species of 

 the genus yet known, from any of our rocks, by having an angular, 

 ascending, and comparatively deep sinus in its pallial line, almost like 

 that seen in many types of the Veneridre. This character is so strongly 

 marked that it was not until 1 had succeeded in getting a tolerably 

 clear idea of the nature of the hinge that I could believe the shell re- 

 lated to the group to which I have referred it. As was pointed out by 

 Mr. Tryon, some years back, the existing American species of Cyrena 

 and Corbicula have the pallial line more or less sinuous; while in 

 nearly all of those from foreign countries it is simple. I have also as- 

 certained that nearly all the extinct North American species yet known 



