I206 CASTAI.IXA 



Castalina nehringi von Ihering. 



Shell short, subrhomboid, somewhat inflated, solid, slightly 

 inequilateral ; beaks full and high with very feeble, radial 

 .sculpture, which does not extend far over the umbonal region ; 

 posterior ridge high and angled above, the shell having its 

 greatest diameter at the ridge, ending in a rounded point behind 

 at the shell's base ; dorsal line short, nearly straight, meeting 

 the obliquely truncate dorsal slope at an angle ; base nearly 

 straight; surface irregularly, concentrically sculptured, with 

 a few wrinkles on the dorsal slope; epidermis dark brown, 

 thick : pseudocardinals radial, nearly smooth ; laterals short, 

 obliquely striate ; beak cavities deep ; nacre dirty white, thick 

 in front. 



Length 57, height 47, diam. 2S mm. 



Southern Brazil. 

 Castalina nehringi von Ihering. Zool. Anz., XIV, 1891, p. 



477; Arch, fiir Nat., 1893, p. 75, pi. iii, fig. 4. — Simpson, 



Syn.. 1900, p. 865. 



A shorter shell than C. iitartotsi; it has higher beaks, a more 

 elevated, sharp posterior ridge, straighter base, and smaller, 

 smoother teeth than that species. The radial furrow behind 

 the posterior ridge is scarcely developed. 



Castalina psammoica (d'Orbigny). 



Shell rhomboid triangular, subinflated, solid, inequilateral; 

 beaks rather full and high, their sculpture consisting of wide, 

 low ridges separated by wide grooves and extending half way 

 over the disk; posterior ridge high, narrowly rounded, ending 

 in a blunt point at the base of the shell ; dorsal line short, 

 lightly arched ; posterior end having a long, oblique truncation ; 

 base a little curved ; anterior end cut away a little above, 

 rounded below ; surface with strong, irregular growth lines 

 and feeble traces of radial sculpture ; epidermis pale brownish 

 or greenish-brown ; pseudocardinals about three in each valve, 

 radial, comparatively smooth ; laterals two in the left valve 

 and one in the right with faint, oblique, granular striation ; beak 

 cavities deep; nacre bluish-white, thickened in front. 



L.ength 68, height 50, diam. 33 mm. 



Tributaries of the Rio de la Plata. 



