124 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



In regard to the geological range of the genus Eriphyla, not very much 

 can be said, in the present state of our knowledge of this and some allied 

 types, beyond the fact that it certainly existed during the Cretaceous epoch. 



i : i- i \t 1: j II ;i gregaria, M . & H. 



Plate 17, figs. 9, a, b. 

 Astarte gregaria, Meek and Hayden (1856), Proceed. Acad. Nat. Sci. Pbilad., VIII, 84. 



Fig. 6. Fig. 7. Shell very small, rather thin, rounded-subtri- 



gonal, a little longer than high, moderately convex; 

 anterior side rounded below and slightly sinuous 

 above ; base forming a nearly semicircular curve ; 

 posterior side more broadly rounded than the 



Lriphyla gregaria. t •" 



Fig. 6. Hiuge and interior of other; dorsum sloping abruptly from the beaks 



right valve, f, being . , viji jv • r i 



fulcrum for ligament. w dh a slightly concave outline in front, convex and 

 Fig. 7. same of opposite valve, declining more gradually behind ; pallial border not 

 crenulate within ; beaks elevated, rather pointed, incurved, approximate, and 

 a little oblique, located slightly in advance of the middle. Surface orna- 

 mented by distinct regular concentric costse and fine obscure lines of growth. 



Length, 0.21 inch ; height, 0.19 inch; transverse diameter of the two 

 valves, 0.14 inch. 



It is not without some doubts that I have referred this little shell to 

 Mr. Gabb's genus Eriphyla,.as it would seem to present some differences in 

 the details of its hinge-characters from the type of that genus; that is, 

 instead of having two well-developed cardinal teeth in the right valve, and 

 only one in the left, it has just the reverse, or, in other words, two in the left 

 and one in the right. In the only specimen showing the hinge of the right 

 valve, seen at the time the above cuts were prepared, there certainly seems 

 to be a slender, shallow, posterior lateral furrow, as if for the reception of 

 the posterior lateral tooth of the left valve, as shown in the above cut, No. 6. 

 In another specimen of the right valve, however, undoubtedly of the same 

 species, the hinge of which has since been worked out, no such posterior 

 lateral furrow is seen, the margin there being merely beveled and prominent, 

 so as to form a long, posterior lateral tooth to fit into the corresponding 

 posterior lateral furrow of the left valve; below the lower end of which 

 furrow there is, in this left valve, a small, posterior lateral tooth, that would 

 seem to fit under the projecting edge of the opposite valve. 



