NEW FRESH-WATER AND MARINE BIViVLVE SHELLS 

 FROM BRAZIL AND URUGUAY 



By William B. Marshall 

 Assistant Curator, Dimsion of MoUusks, United States National Museum 



The Brazilian pearly fresh-water mussel described in this paper 

 came from Areas, Minas Geraes, Brazil, and was presented by Mr. 

 Ralph W. Jackson, of Cambridge, Md. The other four came from 

 Canada Grande, Department of Cerro Largo, Uruguay. These and 

 the three marine shells, which came from the southeast coast of Uru- 

 guay, were presented by Dr. F. Felippone, of Montevideo, Uruguay. 



DIPLODON JACKSONI. new species 

 Plate 4, figures 1-3 



Shell moderately thick, especially in the anterior portion; nearly 

 elliptic, slightly oblique, regularly rounded in front, more sharply 

 rounded at the rear. Dorsal margin gently arched ; ventral margin 

 slightly sloping downward from front to back; posterior margin 

 fusing imperceptibly into the dorsal margin. Surface of the shell 

 with an obscure depression running from the beak to a point just 

 back of the middle of the ventral margin. Beaks set far forward; 

 anterior area small and rapidly descending from the ridge to the 

 anterior margin. Posterior area large; the posterior ridge low and 

 rounded. Sculpture consisting of weak concentric striae, with the 

 rest periods more plainly marked. Color greenish with a metallic 

 luster, especially when the shell is wet. Interior bluish and livid, 

 with but little iridescence. Anterior adductor scars deep and the 

 pedal muscle scars deeply punched; posterior scars superficial. In 

 the right valve there is one long, slightly curved lateral tooth, its 

 summit granulated; and two pseudocardinal teeth set parallel to the 

 anterior dorsal margin, the upper tooth small and platelike, the lower 

 one thicker and fluted on its surface. Left valve with two lateral 

 teeth, and one pseudocardinal nearly divided into two parts by an 

 oblique pit. Pallial line well marked. Beaks with about 20 radiating 



No. 2762.— Proceedings U. S. National Museum, Vol. 74. Art. 17 



5928— 2S X 



