2 PROCEEDINGS OF THE NATIONAL, MUSEUM. vol. 63, 



men from the same place, Cat. No. 347184, U.S.N.M., were received 

 from Dr. A. L. Herrera, director of Estudios Biologicos, City of 

 Mexico. A third specimen from the same locality was returned to 

 Doctor Herrera. 



This species falls into the group of Elliptio semigfanosus v. d. 

 Busch. From that species it differs in being elliptical instead of 

 subtriangular and in nacre and color of periostracum. It is, per- 

 haps, more nearly related to Elliptio distinctus Crosse and Fischer, 

 which, however, has reticulations near the beaks instead of the 

 nodules of the present species. The nacre of distinctus is coppery, 

 and its periostracum is olive-brown, while the nacre of herrerae 

 is white and its periostracum is dark green and chestnut, with 

 many rays. 



DIPLODON (BULLOroEUS ?) PERFRAGILIS. new species. 



Plate 1, figs. 3, 4 ; plate 2, figs. 1-3. 



Shell thin, delicate, translucent, inflated, oblique, narrow in front, 

 broad behind, narrowly rounded in front, widely rounded behind, 

 dorsalline nearly straight, but slightly bending downward in front 

 of the beaks, very lightly winged both anteriorly and posteriorly, 

 beaks located at about the front two-fifths of the dorsal line. Ven- 

 tral margin rounded, posterior dorsal ridge very high, regularly 

 rounded, the posterior dorsal area broad and rapidly descending to 

 the margin. Concentric sculpture consisting of a number of rounded 

 growth ridges, with three rest periods plainly indicated. Beaks 

 each with 14 radiating bars spreading out like the ribs of a fan, no 

 two of them joining into a V as seen in many of the Diplodons^ 

 the ninth bar the stoutest, the eighth and tenth the longest, these 

 two reaching about two-fifths across the surface of the shell. Pe- 

 riostracum nearly smooth, slightly glossy, closely applied showing 

 no tendency to peel, with several radiating wrinkles on the anterior 

 and posterior areas. External coloring uniform light chestnut with 

 a pinkish tint at the beaks. Interior showing the external sculp- 

 ture, the radiating bars of the beaks showing as radiating sulci. 

 Whole interior pinkish, becoming somewhat whitish near the ventral 

 margin, nacre bright but with little iridescence. Pseudocardinal teeth 

 of right valve, two, elongated, thin, joining in a point near the 

 beak, the outer one the smaller, the summit of the inner one slightly 

 overarching the narrow groove between the two. Pseudocardinal 

 of left valve triangular, high, spatulate. The lateral of the right 

 valve is very high at the far end ; the laterals of the left valve long 

 and high, the inner one the longer and higher. 



Type.—Qsit. No. 346801, U.S.N.M. It measures: Length, 28 mm.; 

 height, 20 mm. ; diameter, 15 mm. It comes from the Department 



