220 Bulletin 39 393 



Gatun Stage: Old Harbor. 

 Gatun, C. Z. 



Genus DIPLODONTA, Brown 



Section DIPLODONTA, s. s. 



Diplodonta collina, n. sp. Plate 32, figure 15 



Shell small, subcircular, convex; umbos wide, with small 

 inconspicuous beaks, slightly posterior of the middle; anterior 

 and posterior extremities well rounded into the base forming a 

 part of the same circle; surface sculptured with fine, even, con- 

 centric threads which are nearly lacking from the smooth umbos; 

 hinge normal, and a plain ventral margin. 



Length 6.75, height 6.75, diameter of the right valve 

 1.60 mm. 



A small shell resembling the Diplodonta nucleiformis Wag- 

 ner of the Upper Chesapeake Miocene and the recent West In- 

 dian fauna, but less convex and more finely sculptured. 



Gatun Stage: Middle Creek. 



Section FELAMIELLA, Dall 

 Diplodonta insula, n. sp. Plate 32, figure 21 



Shell small, slightly convex, subcircular; beaks slightly 

 posterior of the middle so that the posterior is a little longer 

 than the anterior; beaks low and inconspicuous; both anterior 

 and posterior extremities widely rounded, the posterior and the 

 ventral margin forming a part of the same circle; surface with 

 fine, concentric threads heaviest on the extremities, but nearly 

 lacking from the umbonal area; interior of shell shallow, the 

 right valve with a strongly bifid posterior cardinal; ventral mar- 

 gin plain. 



lyength 6.60, height 6.50, diameter of the right valve 

 1.25 mm. 



