ART. 3 ]SrEW FOSSIL MUSSELS FROM PERU MARSHALL 6 



diating threads or riblets. Those at the anterior portion are narrow, 

 curved, somewhat granuloiis and do not rapidly increase in thick- 

 ness. Those at the posterior end are also curved but increase rapidly 

 in size. In the middle portion the threads join into several V's with 

 nearly straight sides. The curved threads of the front and rear por- 

 tions if continued would form V's with curving sides. Some of the 

 sculpture shows a tendency to continue into the next area after the 

 distinct umbonal period was passed ; at the anterior end this tendency 

 shows itself in several direct but rather obscure threads which con- 

 tinue across the next growth area. Pseuclocardinal teeth plate-like, 

 nearly parallel to the dorsal margin and close to the tip of the beak. 

 Lateral tooth long and curved. 



The type (Cat. No. 370808, U. S. N. M.) measures : Length, 70 mm. ; 

 height, 39 mm. ; diameter, if both valves were present, would be 

 about 20 mm. A paratype forms Cat. No. 370809, and a paratype was 

 returned to Professor Singewald. They came from Paucarpata, on 

 the Maranon Kiver, and were collected by Dr. Joseph T. Singewald, 

 jr., in whose honor the species has been named. The most striking 

 feature of this species is the neat, clean-cut character of the umbonal 

 sculpture. The species is related to Prodiplodon pauca7'patensis 

 described in this paper, but is less elongate and somewhat more 

 nasute. It is related also to Prodiplodon hassleri Marshall which, 

 however, has an elliptic outline and the beak sculpture pointing 

 differently. The three species form a very natural group. 



PRODIPLODON BASSLERI, new species 



Plate 1, fig. 1 



Shell moderately thin, rather compressed, elliptic, slightly nar- 

 rower in front. Ventral margin regularly curved, rounding regu- 

 larly into the posterior margin, and apparently into the anterior 

 margin also. Posterior ridge low and rounded. Anterior ridge 

 not differentiated from the general surface. Beak set well forward, 

 about 10 mm. behind the anterior margin, and 50 mm. in front of 

 the posterior margin. Sculpture of fairly well-marked concentric 

 striae and lines showing rest periods — the earlier ones set obliquely 

 across the general surface of the shell. Sculpture of umbonal area 

 somewhat obscured but evidently similar to that of Prodiplodon 

 singewaldi but the points of the V's pointing in the general direc- 

 tion of the postero-ventral margin, while in Prodiplodon singeicaldi 

 they are directed toward a point anterior to the middle of the ven- 

 tral margin. Pseudocardinal teeth placed directly under the tip of 

 the beak. Anterior adductor scar very deep, posterior scar nearly 

 superficial. Pallial line at rear end about 10 mm. from the ventral 

 margin. 



