ART. 12 NEW LAND AND FEESH-WATER MOLLUSKS MARSHALL 5 



ehells these rays are quite evident.) Sculpture consisting of three 

 well-marked concentric lines of growth with a number of small 

 concentric striae between them. Beak cavities shallow, with a line 

 of muscle scars at the front portion. Anterior adductor scars deep, 

 with a pair of minor muscle scars back of them ; posterior adductor 

 scars shallow, but perceptible to the touch. Right valve with two 

 pseudocardinal teeth, the inner one large, the outer one very small 

 and platelike, with a narrow groove between the two teeth. The 

 left valve also with two pseudocardinals set obliquely one behind 

 the other and rather ragged. One lateral tooth in the right valve, 

 two in the left valve, all of them obliquely striated in a generally 

 longitudinal direction. Nacre pearl}'^, with scarcely any iridescence, 

 of a generally bluish cast, but with a pinkish or flesh-color tinge in 

 the antero-ventral region. Prismatic border very narrow, less than 

 a millimeter in width. 



The type. Cat. No. 361764, U.S.N.M., measures: Length, 53 mm.; 

 height, 30 mm.; diameter, 15 mm. It comes from the Rio Lempe, 

 Salvador, at the railroad bridge and was collected February 9, 1924 

 by Hildebrand and Foster, under the auspices of the United States 

 Bureau of Fisheries. In addition to the type there are five other 

 specimens. Cat. No. 360388, U.S.N.M., collected at the same time and 

 same place. They are exactly like the type except in size and, in the 

 young specimens, the rays of green color. 



This species is closely related to N efhroyiais roweUii Lea, from 

 which it differs in being much more compressed, in being thinner, 

 in having the beaks nearer the anterior end, and in being more nearly 

 elliptical. 



ELLIPTIC DIVARICATUS, new species 

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



Shell compressed, subrhomboid, rounded and narrower in front, 

 wider, obliquely truncate, and obscurely biangulate posteriorly. 

 Beaks located at about the anterior third of the length. Dorsal 

 and ventral margins slightly curved. Posterior ridge low but prom- 

 inent, slightly riblike to the touch, accentuated by a radiating stripe 

 of color darker than the body of the shell. Color ashy olive, lighter 

 in the anterior portion. Posterior dorsal area with three radiating 

 stripes of smoky tinge, the lowest one on the dorsal ridge. Sculp- 

 ture of four concentric impressed lines marking rest periods in 

 growth and most of the surface covered with radiating, more or 

 less interrupted riblets. At the anterior end the riblets are absent, 

 on the posterior ridge they bifurcate, and on the posterior dorsal 

 area they curve gently toward the margin. Nacre with a light 

 coppery tinge of color, and slightly iridescent in the posterior por- 

 tion. Somewhat thickened in front. Beak cavities shallow. An- 



