FRESH WATER AND LAND SHELLS. 71 



Shell smooth, obovate, rather compressed, pellucid, very inequilateral, rounded and 

 enlarged over the umbonial slope; substance of the shell very thin; beaks slightly promi- 

 nent, minutely undulated at the tip; ligament very short and thin; epidermis dark-brown, 

 and rayed nearly over the whole disk; cardinal teeth single in the right and double in the 

 left valve; lateral teeth double in the right and single in the left valve, long, straight, and 

 lamellar; anterior cicatrices distinct; posterior cicatrices confluent; dorsal cicatrices 

 placed under the plate near to the cardinal tooth; cavity of the shell shallow; cavity of 

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



Remarks. — A single specimen only of this species is before me. It is allied to U. hja/i- 

 nus, described herein, but may be distinguished at once by the form of the teeth, particu- 

 larly the lateral one. which, in that shell, has the remarkable character of being single 

 in both valves. In the hyalinus the carina of the posterior slope is much higher. In the 

 specimen under examination the space about the cavity of the beaks is rubiginose. This 

 may not be a prominent characteristic. The cardinal tooth of the left valve is peculiarly 

 formed, having the superior portion very small, and almost forming a portion of the 

 dorsal line. 



Unio tumescens. PI. III. Fig. 7. 



Tenia I'i'vi, triangulari, injlald; valvulis percraasis, natibus magnis elevatisque; epidermidc tenebroso-fusni, 

 ltd : dt nlibus rardinalibus parvis ; Itihrulibus brevibus, crassis mbcurvisque; margaritd alba et iridescente. 

 Shell smooth, triangular, inflated; valves very thick; beaks large and elevated; epidermis dark-brown, radiated; 

 cardinal teeth small; lateral teeth short, thick and somewhat curved; nacre white and iridescent. 



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



My cabinet and cabinets of Dr. Hale and T. G. Lea. 

 Diam. .1, Length 1.3, Breadth 1.5 inches. 



Shell smooth, triangular, inflated, flattened on the side from the beaks to the margin, 

 angular on the umbonial slope, marly equilateral; substance of the shell very thick. 

 thinner behind; beaks large and elevated; ligaments short and thick; epidermis dark- 

 brown, finely striate, and with green rays reaching to the margin; cardinal teeth small, 

 and rather erect ; lateral teeth short, thick, and somewhat curved, thickened at the pos- 

 terior end; anterior cicatrices distinct; posterior cicatrices distinct; dorsal cicatrices 

 placed under the cardinal tooth; cavity of the shell shallow, cavity of the beaks -hallow 

 and rounded; nacre white and iridescent. 



Remarks. — This species is allied to / '. tri»<»ins, (Nobis,) and /. Edguriamis, (Nobis,) 

 and somewhat resembles U. obliquus, I. am. It differs from trigonus in being more rounded 

 and in having rays. It is fuller than Edgarianus, and is rayed Bomewhat like it. I have 

 but one perfect, specimen and a single odd valve of this species, and in all these three 

 valves the superior posterior cicatrix is remarkably dee]) and round. 



I MIO PEENODOSUS. PI. III. Fig. 8. 



Testa pernodosd, rotunda/a, subcompressd ; valvulii crassis} nut bus elevaiit; epidermide htfeo-JutcAf (ln) 

 tibus cardintdibus magnis; latcralibus brevibus, crassis subrcclisrjue ; margaritd albd. 



