CHIEFLY OF THE UNITED STATES. 61 



Shell closely and delicately sulcate, elliptical, somewhat inflated, very inequi- 

 lateral, obtusely angular behind and rounded before ; substance of the shell a little 

 thick, somewhat thicker before ; beaks slightly prominent, with radiating undula- 

 tions at the tips; ligament rather long, thin and dark brosvn ; epidermis dark brown, 

 nearly black, without rays and with rather distant marks of growth ; umbonial slope 

 raised and rounded; posterior slope narrow, elliptical, carinate, with obscure im- 

 pressed lines from the beaks to the posterior margin ; cardinal teeth small, very 

 much compressed, oblique, abrupt at the end, single in the left and double in the right 

 valve ; lateral teeth very long, lamellar and nearly straight ; anterior cicatrices 

 confluent, rather small and slightly impressed ; posterior cicatrices confluent, rather 

 large and very slightly impressed ; dorsal cicatrices in a row across the centre of the 

 cavity of the beaks ; cavity of the shell rather shallow and wide ; cavity of the beaks 

 very shallow and rounded ; nacre white and very iridescent. 



Remarks. — Several specimens were among the shells sent to me by the Smithso- 

 nian Institution for examination. Like many Asiatic species, it has the double 

 cardinal tooth in the right and the single one in the left valve. In the lateral tooth 

 of the left valve the upper branch is very much the smaller. The undulations of the 

 tips of the beaks do not diverge from the apical point, as is usual with the South 

 American species, but two sets meet in the centre and form an angle. In outline 

 this species is very close to U. Wilsonii, (nobis,) but the two species differ much in 

 color of epidermis and in the beaks. 



Unio Pazii. pi. 21, fig. 60. 



Testa Isevi, obliqua, antice inflata, valde insequilaterali, postice acuto-angulata et attenuata, antice rotun- 

 data ; valvulis crassiusculis, postice aliquanto crassioribus ; natibus tumidis, subterminalibus ; 

 epidermide olivacea, obsolete radiata et transverse late vittata ; dentibus cardinalibiis longis, lamella- 

 tis, valde obliquis corrugatisque ; lateralibus prselongis, obliquis, lamellatis corrugatisque ; margarita 

 vel alba vel caerulea et valde iridescente. 



Shell smooth, oblique, inflated before, very inequilateral, acutely angular and 

 attenuate behind, rounded before; valves somewhat thick, slightly thicker before; 

 beaks swollen and nearly terminal ; epidermis olivaceous, obscurely rayed and 

 transversely broadly banded ; cardinal teeth long, lamellar, very oblique, corrugate ; 

 lateral teeth very long, oblique, lamellar and corrugate ; nacre white or bluish and 

 very iridescent. 



Proc. Acad. Nat. Sci., 1862, p. 176. 

 Eah. — China, Don Patricio Maria Paz, of Madrid ; Siam, W. D. Hartman, M. D. 

 My cabinet and cabinets of Don P. M. Paz and Dr. Hartman. 

 Diam. -9, Length Tl, Breadth 2-4 inches. 



16 



