DIIT.ODON 1235 



DiPLODON RUDus (Lea). 



"Shell smooth, elliptical, thick, iiiHated, inequilateral, emar- 

 ginate behind, obliquely rounded, before ; substance of the shell 

 thick and ponderous, thicker before ; beaks thick and promi- 

 nent ; ligament rather short, thick and light brown ; epidermis 

 dark brown, lighter towards the beaks, roughly striate, the 

 marks of growth being rather close and irregularly impressed 

 into furrows, which are crossed by a few, indistinct, impressed 

 furrows from the beaks to the margin ; umbonal slope raised 

 and rounded ; posterior slope broad, rather flat, with a low 

 keel rising from a deep, broad furrow ; cardinal teeth rather 

 small, somewhat elongate, striate, crenulate, and double in 

 both valves ; lateral teeth somewhat long, rather thick, granu- 

 late, thickened towards the end and curved ; anterior cicatrices 

 distinct, large and deeply impressed ; posterior cicatrices con- 

 fluent, rather large and well impressed ; dorsal cicatrices well 

 impressed and placed in a row across the centre of the cavity 

 of the beaks ; pallial cicatrix irregular and deeply impressed ; 

 cavity of the shell deep and rounded ; cavity of the beaks 

 rather deep and subangular ; nacre white, disposed to be pink- 

 ish at the anterior margin and iridescent. 

 Length 3, height 2.2, diam. 1.4 in." (Lea). 

 Rio de la Plata. 

 Unio rudus Le.\, Pr. Ac. Nat. Sci. Phila., IH, 1859, p. 187; 

 Jl. Ac. Nat. Sci. Phila., IV, i860, p. 266, pi. xi.iii, fig. 146; 

 Obs., VII, i860, p. 84. \-)\. xLiu, fig. 146. — KusTER, Conch. 

 Cab. Unio, 1861, p. 261, pi. i.xxxviii, fig. i. 

 Margaron fUnio) rudus Lea, Syn., 1870, p. 50. 

 Unio rudis P^tel, Conch. vSam., Ill, 1890, p. 166. 

 Diplodon rudus Simpson, Syn., 1900, p. 875. 



"There was a single specimen only of this species sent to 

 me by Dr. Von dem Busch. It is much stouter than Uniones 

 are usually from South America, and perhaps is more nearly 

 allied to zvheatleyanus, (nobis), from the Rio Negro than any 

 other species. It approaches to delodontus Lam., but is thicker 

 and more rotund than that species. It may be distinguished 

 at once from ivheatleyanus by its greater thickness, by the 



