NO. 2209. yEW MU^til'JLS OF Till:: UEXU/S Dl I'LODOX— MARSH ALL. 387 



much eroded. Surface with many fine lines of growth and with four 

 rest periods indicated by dark lines. Numerous well-marked striae 

 radiate from the beaks to the ventral margin. Periostracum dark 

 broAvn, somewhat bronzy, scarcely shining, darker at the posterior 

 end. Nacre hvid in the upper portion, white below, brilliant pos- 

 teriorly, thickened anteriorly, iridescently radiately striate. Pseudo- 

 carduials of right valve long, low, the u]>per the smaller, tlie groove 

 between them slightly curved. Pseudocardinal of the left valve plate 

 like, standing on a narrow shelf, thin at its upper end, thickened at 

 the lower end. Lateral tooth of right valve long, low, and granulous. 

 Laterals of the left valve nearly equal, the groove between them 

 widening at the rear. 



Tiie type (pi. 55, figs. 1-4) is one of three specimens of Cat. No, 

 162383, U.S.N.M., from Rio Itapoca, Brazil, received from Dr. 11. von 

 Ihering. It measures — length, 63 mm., height, 33 mm., diameter 

 18 mm. Plate 52, figure 6, shows the beak (enlarged three diameters) 

 of a specimen from the same locaUty and with the same catalogue 

 number. 



DIPLODON SEMIGRANOSUS Simpson. 



Plate 55, figs. 5-8. 

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

 Fresh-water Mussels, 1914, p. 1252. 



Shell rather small, irregularly long elliptical, sharply rounded in 

 front, somewhat nasute behind. Ventral margin regularly curved. 

 Posterior ridge rounded, scarcely developed. Beaks apparently low, 

 .eroded, retaining vestiges of radial, somewhat granular, sculpture. 

 Surface with feeble growth lines and three or four rest periods indi- 

 cated by dark lines. Numerous faint, slightly granular striae radiate 

 from the beaks, giving the surface a semigranulous appearance, 

 especially anteriorly. 



Periostracum thin, closely adhering, olivaceous, tinged with 

 greenish, somewhat glossy. Nacre dirty bluish-white, thickened 

 along the forward portion of the ventral margin, thin and iridescent 

 posteriorly. Pseudocardinals of right valve moderately thick, 

 parallel, the groove between them wide and deep. Pseudocardinal 

 of left valve thm and plate-like. Lateral tooth of right valve mod- 

 erately high. The upper lateral of the left valve low and weak, the 

 lower one higher and moderately strong. 



The type (pi. o5, figs. 5-8) is one of 11 specimens of Cat. No. 128790, 

 U.S.N.M., from Rio Tiete, Sao Paulo, Brazil, from Dr. H. von Ihering. 

 It measures — length, 47 mm.; height, 26 mm.; diameter, 15 mm. 



Cat. No. 162414 includes two and No. 162415 one specimen from 

 Ponte Grande, Sao Paulo, No. 162413 one specimen from Os Perus, 

 Sao Paulo; No. 162412 six specimens from Ponta Grossa, Parana. 

 All these localities are in southern Brazil and all the specimens were 

 received from Dr. von Ihering. 



