347 Costa Rica Miocene— Oi^sson 175 



beaks very small and scarcely distinguishable from above, and 

 situated nearly about the middle of the dorsal margin; extremi- 

 ties bluntly rounded, with a broad, even curve to its base or ven- 

 tral margin; the dorsal side is nearly straight but descending 

 slightly towards its extremities; surface nearl}' smooth, the 

 growth lines indistinct, but with fine, even very slightly oblique 

 lines on the anterior two-thirds of the shell; interior con- 

 cealed. 



Length 54.00, height 15.00, diameter 4.50 mm. 



Differs from the preceding species by its larger size, nearly 

 central beaks and b}' its finer, more concentric sculpture. There 

 are several species of this group recent in the- West Indies and 

 along the Pacific coast of Central America, but none appear at 

 all closely related to the Gatun species. 



Gatun Stage: Hill ATo. j, Banana River. 



Leda Dalliana, n. sp. Plate 28, figure 17 



Adrana sp ? Dall, 1898, Trans. Wagner Free Inst. Sci., vol. 3, pt. i 

 4, P- 592. 



Shell small, thin, elongate, depressed; the small, scarcely 

 differentiated beak is sutuated about the anterior one-fourth of 

 the shell; the anterior side is somewhat contracted and shortly 

 rounded while the posterior side is produced and 3 times the 

 length of the anterior and bluntly pointed at its extremity; the 

 rostrum is long and narrow, formed by 2 radial, scabrous threads, 

 separated by a wide interspace; concentric sculpture of thin, 

 elevated threads or lamellae, regularly distributed on the lower 

 half of the shell, but widely spaced on the umbonal area; the 

 escutcheon is long and narrow, sculptured wath threads parallel 

 to the hinge-margin; interior of shell cavity shallow, the long 

 hinge with an anterior set of 20 small teeth, the posterior with 

 26 or 27. 



Length 10.50, height 3.50, diameter of left valve .75 mm. 



