386 PROGEEDINGii OF THE NATIONAL MUSEUM. vol.53. 



DIPLODON TRIVIALIS Simpson. 



Plate 54, figs. 5-8. 



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

 Fresh-water Mussels, 1914, p. 1250. 



Shell obovate, moderately inflated, subsolid, evenly rounded before 

 and behind, narrower in front. Dorsal and ventral margms curving. 

 Posterior ridge rounded, scarcely developed. B'eaks moderately ele- 

 vated, somewhat eroded, but showing that the sculpture consisted of 

 about 20 radiating bars. Surface with a number of feebly marked 

 growth lines, with four rest periods, indicated by dark Imes. Faint 

 indications of radiating striae on nearly the whole surface. Perios- 

 tracum scarcely shining, clothlike, very dark olivaceous chestnut,* 

 closely adhering. Nacre bluish-white, somewhat iridescent, thickened 

 along part of the ventral margin. Pseudo cardinals of right valve 

 parallel to each other, the upper one low, small and Imear. The lower 

 one thick, triangular, set at an angle of about 50 degrees with the 

 lateral. Pseudocardinals of left valve distinctly two, subequal, set at 

 an angle with each other. Lateral of right valve thin and high. 

 Laterals of left valve subequal, the groove between them rather deep 

 and wide. 



The type (pi. 54, figs. 5-8), Cat. No. 162409, U.S.N.M., measures- 

 length, 51 mm.; height, 33 mm.; diameter, 19 mm. It comes from 

 Taboticabal, Sao Paulo, Brazil, and was received from Dr. H. von 

 Ihering. Cat. No. 162406 includes two specimens and Cat. No. 162411 

 includes one specimen, ail from the same source as the type. Cat. 

 Nos. 125739, 162407, and 162408 each include one specimen from 

 Piracicaba, Sao Paulo, Brazil, from Dr. von Ihering. Cat. No. 125703 

 includes one specimen from Rio Grande do Sul, Sao Paulo, Brazil, 

 from Mr. B. H. Wright. 



Mr. Simpson at first identified all of the above as Diplodon peculiaris 

 Lea, but later came to the conclusion that they belonged to a new 

 species. The collection contains the type of peculiaris, with which I 

 have compared the type of trivialis, and I believe the two are distinct. 

 Figure 6 shows the sculpture of the beaks. Tiie rays are finer, more 

 numerous, occupy a smaller area, and are more nearly parallel than 

 those of peculiaris. 



Tv\'o of the eight specimens in the collection have two lateral teeth 

 in each valve. The other six specimens have a single lateral in the 

 right valve and tv»-o laterals in the left valve. 



DIPLODON SANTA MARIAE Simpson. 



Plate 52, fig. 6; plate 55, figs. 1-4. 

 Diplodon sania mariae Simpson, A Descriptive Catalogue of the Naiades or Pearly 

 Fresh-water Mussels, 1914, p. 1270. 



Shell oblong, rhomboid, nearly twice as long as wide, moderately 

 thin. Ventral and dorsal margins nearly parallel. Posterior ridge 

 low, rounded, biangulate. Posterior margin biangulate. Beaks low, 



