82 DESCRIPTION OF NEW 



confluent; posterior cicatrices distinct; dorsal cicatrices placed on the under side of the 

 plate near the cardinal tooth; cavity of the shell deep and rounded; cavity of the beaks 

 very shallow and rounded; nacre pearly white and very iridescent. 



Remarks. — A single specimen only of this small species was procured by Dr. Budd. It 

 is nearly allied to U. castaneus, Nobis, but may be easily distinguished from it by its not 

 being oblique, and in having the umbonial slope angular. The cardinal teeth are also 

 very much smaller. 



Anodonta tetragona. -PI. VIII. Fig. 25. 



Testa hevi, oblongd, valde inflatd; valvulis tenuibus; natibus prominulis ; cpidermide luteo-fuscd, radiatd ; 

 , arearitd cseruleo-albd el iridescente. 



Shell smooth, oblong, much inflated; valves thin; beaks somewhat prominent; epidermis yellowish-brown, 

 r.ived; nacre bluish-white and iridescent. 



Hab. Alexandria, Louisiana. J. Hale, M. D. 



My cabinet and cabinet of Dr. Hale. 

 Diam. 1.00, Length 1.4, Breadth 2.2 inches. 



Shell smooth, oblong, very much inflated, subangular on the umbonial slope, inequilate- 

 ral, incurved on the dorsal margin, angular behind; substance of the shell very thin; beaks 

 somewhat prominent; ligament rather long and thin; epidermis yellowish-brown, with 

 numerous indistinct rays; anterior cicatrices confluent; posterior cicatrices confluent; 

 dorsal cicatrices immediately over the centre of the cavity of the beaks; cavity of the 

 shell deep and rounded; cavity of the beak rather deep and angular; nacre bluish-white. 



Remarks. — Among the shells sent to me by Dr. Hale, was a single specimen of this 

 species, which, though nearly allied to Mr. Say's cdetdida, may be easily distinguished by 

 its angular umbonial slope. The rudiments of a cardinal tooth are quite as prominent, if 

 not more so, than in the edentula, which, when described by Mr. Say, he considered to 

 belong to his genus Alasmodonla. The lines of growth in tetragona are distinct and 

 distant, and the basal margin in the interior is somewhat rubiginose. 



Margaritana minor. PI. VIII. Fig. 26. 



Testa Isevi, triangvlari, compressd ; valvulis tenuibus; natibus prominulis, ad apices undulatis; cpidermide 

 virido-lutea } denlibus cardinalibus parvis ; margarijd cseruleo-albd el iridescente. 



Shell smooth, triangular, compressed ; valves thin; beaks slightly prominent, undulated at the beaks; cardinal 

 teeth small; nacre bluish-white and iridescent. 



1 bib. Tennessee— S. M. Edgar, M. D. North Carolina— B. W. Budd, M. D. 

 Diam. .5, Length .7, Breadth 1.2 inches. 



Shell smooth, triangular, compressed, obtusely angular on the umbonial slope and flat- 

 tened on the side, inequilateral; substance of the shell very thin and somewhat trans- 

 parent, thicker before than behind; beaks slightly prominent and minutely undulate at the 

 tips; ligament very short and very thin; epidermis greenish-yellow, greener on the pos- 

 terior portion, with minute stria-; cardinal teeth very small and somewhat pointed; 



