290 REPORT UNITED STATES GEOLOGICAL SURVEY. 



Cyrena inflexa Meek. 



Plate 10, figs. 7 a and 6. 

 Corbicula ( Veloritina) inflexa Meek, 1871, An. Rep. U. S. Geol. Snrv. Terr, for 1872, p. 493. 



The figures of this species on plate 10 were drawn from Mr. Meek's 

 types, and the following - is a copy of bis original description: 



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

 long, moderately convex ; posterior extremity rather narrowly rounded, 

 or apparently sometimes faintly truncated; 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 mnbonal 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 im- 

 pression larger and obscure ; pallial hue showing a deep, angular, ascend- 

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

 or qidte 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.G8 inch. 



"Locality and position. — Near Missouri Eiver, below Gallatin City, 

 Mont., where it occurs associated with Trigonia, Inoceramus, Cardium 

 Ostrea, and other marine Cretaceous fossils." 



Mr. Meek referred this shell to the genus Corbicula and his subgenus 

 Veloritina. It is almost certainly not Corbicitla, as that genus is usually 

 restricted, because its lateral teeth are not transversely striated, and its 

 pallial sinus is very different. As remarked in connection with the 

 description of the preceding species, I refer such shells as that and this 

 one to Cyrena, if found associated with marine Cretaceous species and 

 the lateral teeth show no striatum. The character of the lateral sinus, 

 however, as pointed out by Mr. Meek, is very hke that of the Veneridce, 

 and not like that of either Corbicula or Cyrena, and it is likely that this 

 shell does not properly belong to either of those genera. But until we 

 can obtain specimens which show clearly the character of all parts of 

 the hinge, I prefer to refer such forms as this to Cyrena, as before stated. 



Genus COEBULA BruguiCre. 



CORBULA NEMATOPHORA Meek. 



Plate 3, figs. 4 a, b, c, and d. 



CorbuJa nemaiophora Meek, 1873, An. Rep. U. S. Geol. Surv. Terr, for 1872, p. 496. 

 Corbula nematophora Wliite, 1876, Expl. & Surv. West of 100th Merid., vol. iv, p. 188, 

 pi. xvii, fig. 7. 



" Shell of about medium size, ovate-subtrigonal, nearly equivalve and 

 moderately convex, with height equaling two-thirds the length ; anterior 

 outline rounded; base semi-ovate; posterior extremity somewhat pro- 

 duced and subangular or minutely truncated in outline below ; dorsal 

 outline sloping from the beaks, the anterior slope being more abrupt and 

 slightly concave in outline above, and the posterior longer and nearly 

 straight, with a greater obliquity ; posterior umbonal slopes more or less 

 angular in each valve, from the beak to the posterior basal extremity ; 

 beaks rather prominent, and placed about one-third the length of the 



