CHIEFLY OF THE UNITED STATES. 265 



Hab. — Buenos Ay res, South America, Don Patricio M. Paz. 



Mj cabinet and cabinet of Don. P. M. Paz. 

 Diam. -8, Length 1-2, Breadth I'S inch. 



Shell smooth, elliptical, very much inflated, inequilateral, somewhat rounded be- 

 hind and subtruncate before ; substance of the shell thin ; beaks rather prominent, 

 swollen, with divergent folds at the tips ; ligament very small and light brown ; 

 epidermis dark brown, obscurely rayed, with distant marks of growth, striate on the 

 anterior half; umbonial slope rounded and very much inflated; posterior slope ellip- 

 tical, rather wide, with an indistinct furrow in each valve ; cardinal teeth small, very 

 much compressed, very oblique and double in both valves ; lateral teeth rather small, 

 nearly straight, thin and lamellar ; anterior cicatrices confluent and slightly impres- 

 sed; posterior cicatrices confluent and scarcely visible; dorsal cicatrices placed above 

 the centre of the cavity of the beaks; cavity of the shell deep and wide; cavity of 

 the beaks very shallow and rounded ; nacre bluish white and iridescent. 



Bemarlcs. — Of this well characterised little species there was only a single specimen 

 received. In outline it is near to Bengalensis (nobis), but it is more inflated, has 

 larger teeth and a thicker and white nacre. It differs from ampullaceus, herein de- 

 scribed, in being elliptical, more inflated over the umbones, and being a much lighter 

 shell. The beaks well display the divergent folds at the tij^s, a character so well 

 denoting its South American origin. 



Unio peculiaris. pi. 34, fig. 80. 



Testa Iffivi, quadrata, compressiuscula, insequilaterali, postice obtuse angulata, autice rotuuda ;. val- 

 vulis crassiusculis, antice aliquauto crassioribus ; Eatibus subprominentibus, ad apices divaricate 

 iindulatis, ; epidermide vii'idi-fusca, eradiata ; dentibus cardinalibus parviusculis, compressis, ob- 

 liquis, ia utroque valvulo duplicibus ; lateralibus longis, lamellatis curvisque; margarita creruleo- 

 alba et iridescente. 



Shell smooth, quadrate, somewhat compressed, inequilateral, obtusely angular be- 

 hind, round before ; valves a little thick, somewhat thicker before ; beaks a little 

 prominent, with divergent folds at the tips; epidermis greenish-brown, without rays; 

 cardinal teeth rather small, compressed, oblique and double in both valves ; lateral 

 teeth long, lamellar and curved; nacre bluish white and iridescent. 

 Proc. Acad. Nat. Sci. 1866, p. 33. 



Hah. — South America, Don Patricio M. Paz. 



My cabinet and cabinet of Don. P. M. Paz. 

 DIam. -9, Length 1-3, Breadth 2 inches. 



Shell smooth, quadrate, somewhat compressed at the sides and inflated on the um- 

 bonial slope ; inequilateral, obtusely angular behind, round before ; substance of the 

 shell somewhat thick, slightly thicker before ; beaks a little prominent, slightly in- 



