NO. 2209. NEW MUSSELS OF THE GENUS DIPLODON— MARSHALL. 385 



one odd valve (Cat. No. 150390 U.S.N.M.) were sent by Doctor Rush 

 from the same place. 



A lot of South American naiades just identified for Doctor Felippone 

 includes 27 specimens of this species, of various ages, from localities 

 in Uruguay. The two largest and oldest specimens measure, re- 

 spectively — length, 91 mm.; height, 47 mm.; diameter, 27 mm.; and 

 length, 86 mm.; height, 46 mm.; diameter, 29 mm. The old speci- 

 mens retain all the typical characters, and vary from the younger 

 specimens only in the thickening and enlarging of the pseudocardinal 

 teeth. As is well known, a similar thicking and enlarging of these 

 teeth is a common, almost a usual, occurrence in old specimens of 

 the naiades in general. 



DIPLODON SUPPOSITUS Simpson. 



Plate 51, fig. 2; plate 54, figs. 1-4. 



Diplodon suppositus Simpson, A Descriptive Catalogue of the Naiades or Pearly 



Freeh-water Mussels, 1914, p. 1245. 

 Diplodon piceus (part) Simpson, Synopsis, 1900, p. 877. 



Shell moderately thin to subsolid, thinner posteriorly, slightly 

 thickened anteriorly. Outline subrhomboidal, regularly rounded in 

 front, bluntly round-pomted behind. Dorsal and ventral margins 

 nearly parallel, the ventral margin slightly arcuate. Posterior dorsal 

 ridge nearly wanting and, hence, the posterior dorsal area not dis- 

 tinctly marked off from the general surface of the shell. Beaks low, 

 eroded in the type. Surface of shell with many poorly marked 

 growth lines, obscurely showhig four rest periods. Anterior portion 

 with faint radial striae. Epidermis chestnut, bronzy. Nacre bluish 

 white or livid, nearly dull anteriorly, briUiant posteriorly. Radiating 

 striae show through the nacre at the posterior third. Pseudo- 

 cardinals of right valve two, thin, parallel, set at an angle of about 

 sixty degrees with the lateral. In the left valve the pscudocar- 

 dinals are not sharply defined into two. Lateral teeth two in the 

 left valve, one in the right valve. 



The type (pi. 54, figs. 1-4) measures — length, 49 mm.; height, 26 

 mm.; diameter, 14 mm. It came from Parana, Brazil, and is one 

 of four specimens bearing Cat. No. 162374, U.S.N.M. 



Plate 51, fig. 2, represents the beak of this species, enlarged three 

 diameters. The specimen figured comes from Rio Tiete, Brazil, 

 and is one of three specimens m the United States National Museum 

 (Cat. No. 128824). Both the specimens figured were received from 

 Dr. II. von Ihering. 



In addition to the specimens mentioned above the collection con- 

 tains twelve other lots including 26 specimens, all from localities in 

 Southern Brazil. All these were identified by Simpson as belonging 

 to D. suppositus. 



77403— Proc. N. jM. vol. 53—17 25 



