1282 DIl'I.ODON 



Unio gratits Li;a, Pr. Ac. N. Sci. Phila., IV, i860, p. 91 ; Jl. 



Ac. N. Sci. Phila., V, 1863, p. 382, pi. xltii, fig. 290; Obs., 



X, 1863, P- 18, pi. xijTT, fig-. 290. — SowERCY, Conch. Icon., 



XVI, 1868, pi. Lxxxiv, fig. 444. 

 Mar gar on (Unio) grains Lea, Syn., T870, p. 56. 

 Diplodon gratiis Simpson, Syn., 1900, p. 886. 



After critically comparing the type of Unio grains Lea and 

 a large amount of additional material with d'Orbignv's de- 

 scription and figure of Unio fontainiana and with what I con- 

 sider authentic specimens of that form, I believe that they are 

 mere varieties of the same thing. Lea's shell diflfers in being 

 lighter colored and perhaps a little sharper on the post-dorsal 

 angle, but the other characters seem to agree ver}- well through- 

 out. 



Diplodon roiundus (Wagner). 



Shell short obovate or subtriangular, subcompressed to 

 slightly inflated, subsolid, inequilateral ; beaks somewhat ele- 

 vated, their sculpture a few, short, radial bars; post-dorsal 

 slope raised into a low wing and more or less abruptly trun- 

 cated behind ; anterior end narrowed and rounded ; post-basal 

 region much produced ; surface sculptured with fine, uneven 

 concentric striae, and having traces of radial sculpture ; epi- 

 dermis olive or brownish with a soft smoky tint, feebly rayed 

 in young shells ; left valve with two compressed pseudocardi- 

 nals, the hinder smaller, and two curved laterals; right valve 

 with two pseudocardinals and one lateral ; dorsal scars few 

 and deep ; muscle scars small, shallow ; nacre bluish-white, sil- 

 very and iridescent behind, a little thicker in front. 



Length 2,7, height 2,2 mm. (figured type). 



Length 67, height 55, diam. 28 mm. 



Length 70, height 34, diam. 33 mm. 



Brazil. 

 Unio rohindiis Wagnkr. Test Kluv. Bras., 1827, p. 34, pi. xxv, 



figs. 3, 4. — MoRTCAND, Mem. His. Soc. Gen., 1838. p. 49, pi. 



IV, figs. T2-14. — KusTER, Conch. Cab. Unio, 1856, p. 160. pi. 



XLVi. figs. I, 2. — SowERRY, Conch. Icon., XVI, 1868, pi. 



j.xxTi, fig. 369. 



