STANTON.] 



CYRENIDiE. 101 



rocks of the West, but the prominent umbonal ridge, and the coarser 

 and nonspiniferous costsB of that species, besides many other details, 

 clearly separate it from the species here described; the peculiar char- 

 acter of the surface markings also separate it from any other described 

 species with which it is in any danger of being confounded. 



" Position and locality. — Cretaceous strata, probably equivalent with 

 the lower portion of the Colorado group; head of Waterpocket canyon, 

 southern Utah. Collected by Mr. G. K. Gilbert." 



CYRENID^E. 



Genus CYRENA Lamarck. 

 Oyrena (Veloritina) seouris Meek. 

 PI. xxitt, Figs. 1-3. 



Corbicula (Oyrena?) securis Meek, 1873, Aim. Kept. U. S. Geol. Sur. Terr, for 1872, p. 



494; White, 1879, idem for 1877, p. 289, PI. 3, Fig. 2, a, b, c. 

 Cyrena ( Veloritina) erecta White, 1876, Geol. Uinta Mts., p. 117. 

 Compare Cyrena (Veloritina) durkeei (Meek) White. 1876, U. S. Gcog. and Geol. Surv. 



West 100th Meridian, vol. IV, p. 207, PI. 21, Figs. 13a, b. 



The original description was based on an internal cast. Near the 

 same locality Dr. White obtained well preserved examples which he 

 described as follows : 



" Shell of medium size, obliquely subovate in marginal outline when 

 adult, but subcircular when young, gibbous, especially the upper 

 median portion, but somewhat laterally compressed at the postero- 

 basal portion; an tero -basal, basal, and posterobasal borders forming a 

 continuous, almost regular, curve; the dorsal outline, by lateral view, 

 also broadly rounded from the beaks to the posterobasal border; front 

 a little concave transversely below the beaks, and also vertically con- 

 cave from the beaks to a point a little below themidheightof the shell; 

 beaks prominent, approximate, and curved forward; ligament short 

 and narrow. This concavity of the dorsum resembles an escutcheon, 

 except that it is not defined, especially at the ends; it is moderately 

 deep, narrow, and bounded at the sides by the abrupt rounding inward 

 and downward of the surface from the outer side of each valve, so that 

 the hinge margin is wholly hidden from sight by a side view of the 

 shell; hinge and interior unknown. Surface marked by the ordinary 

 lines and imbrications of growth. 



"Height, 33 mm ; anteroposterior width the same; thickness about 

 22 mm ." 



The additional specimen now before me, though slightly crushed just 

 behind the beak, shows the larger part of the hinge. There are three 

 rather small, slightly divergent cardinal teeth (in the left valve) of 

 which the middle one is somewhat larger than the others. The lateral 

 teeth are long and prominent, apparently not striate. 



