CRETACEOUS FOSSILS. 169 



diverging cardinal teeth, and more strongly striated laterals. Its surface is 

 also rougher, being more strongly furrowed and ridged than that of our shell, 

 and its lunule is much larger. 



Deshayes has noticed, in his later work on the Paris Basin fossils, the 

 points of resemblance between the latter of the above-mentioned species 

 and the existing genus Velorita, and yet points out some differences that 

 indicate a transition from the typical forms of Corhicula toward Velorita, 

 through such species as C. antiqua. The species here under consideration 

 seems to me also to occupy a somewhat intermediate position between the 

 two genera mentioned, having more nearly the trigonal form, oblique car- 

 dinal teeth, and thick solid shell of Velorita, while its anterior lateral teeth 

 are as elongated and slender as in Corhicula. It, however, differs from both, 

 in the pecuHar incurved character of the posterior dorsal edges of its valves, 

 so as to form a very deep concavity or furrow along their entire length, as seen 

 when the valves are united. This inflection of the borders and the depressed 

 nature of the ligament, bring the latter so far below the elevated umbonal 

 slopes that it is entirely hidden from view in looking at the shell from either 

 side, instead of projecting above the umbonal slopes, as in the two types 

 above mentioned. Again, the posterior lateral tooth of its left valve is some- 

 times mainly foi'med by beveling of the inflected edge of the valve, instead 

 of projecting out at right angles to an erect margin. In consequence of 

 these peculiarities of our shell, I have already proposed to make it the type 

 of a new section, under the name Veloritina, in Dr. Hayden's Report of 

 1872. Whether or not this section can properly include Cyrena antiqua, I 

 am not well enough acquainted with that shell to decide ; but, although it 

 seems to depart from our type in some of its distinguishing characters, I am 

 inclined to believe that it may find a place in the same group. 



Locality and position. — The first specimens of this species that I have seen, 

 were brought from the brackish- or fresh- water beds on Sulphur Creek, near 

 Bear River, "Wyoming. Soon after, Mr King's party brought in additional 

 specimens from the same locality and beds; and, at a later date, Mr. Durkee, 

 an engineer on the Union Pacific Railroad, sent numerous specimens of it 

 and the associated fossils to the Smithsonian Institution, for the use of which 



