ART. 16. NEW FRESH WATER MUSSELS MARSHALL. 6 



tander, Colombia. They were presented by Dr. C. Wythe Cooke, of 

 the Geological Survey, who collected them in April, 1920, and in 

 whose honor the species is named. 



The sculpture of the exterior is remarkable and of great beauty. 

 The radiating striae between the impressed radiating lines are of a 

 fineness rarely if ever equaled in shells with the rude structure of the 

 naiads. 



DIPLODON SUBCYLINDRICUS, new species. 



Plate 2, figs. 1, 2 ; plate 3, figs. 1. 2, 11. 



Shell long, nearly elliptical, anterior end regidarly rounded, pos- 

 terior end nearly regularly rounded but obscurely bluntly angled 

 near the lower side, ventral and dorsal margins subparallel. Both 

 the anterior and posterior ridges full and rounded, the descent to 

 the dorsal margins very abrupt, giving the shell a gibbous form. 

 Beaks not very high, with 15 rather coarse radiating ribs. Surface 

 rather smooth, with many concentric lines of growth. Periostracum 

 closely adhering, slightly glossy. Color nearly uniform chestnut. 

 Nacre silvery white. Pseudocardinals of right valve two, platelike, 

 very long, the inner one beginning near the beak and reaching al- 

 most to the adductor scar, the outer one nearly as long, slightly over- 

 topping the inner one. Left valve with but one pseudocardinal 

 which is very long, somewhat paddle-shaped, very thin and slightly 

 bent upward. Eijiht valve with one lateral tooth which is some- 

 what distant from the beak and has its posterior end roughened. 

 Laterals of left valve quite distant from the beak, short, incon- 

 spicuous. 



The type (Cat. No. 341375, U.S.N.M.) measures: Length 82 mm., 

 height 35 mm., diameter 42 mm. It comes from Arroyo Manga, 

 Department of Montevideo, Uruguay. Other specimens in the col- 

 lection, all from Uruguay, are as follows: A right valve from the 

 Department of Canelones (Cat. No. 335776) ; a specimen from 

 Arroyo Sauco in the same Department (Cat. No. 331282) ; a right 

 valve from Maldonado, Department of Maldonado (Cat. No. 

 335775). All the above-mentioned specimens were collected and pre- 

 sented by Dr. Florentino Felippone. 



The nearest relative of this species is DiploJon piceus Lea, which 

 however, is much smaller, proportionally thicker, has a black epi- 

 dermis, and differs in the character of the teeth. 



DIPLODON SUBQUADRATUS, new species. 



Plate 2, figs. 6, S ; plate 3, figs. 8-10. 

 Shell subquadrate, moderately inflated, moderately thick, broadly 

 truncated posteriorly, narrowly truncated anteriorly. Anterior and 

 posterior dorsal areas compressed ns if pinched, posterior ridge 

 20107— 22— Proc. N. M. vol. 61 23 



