CHIEFLY OF THE UNITED STATES. 



269 



species, with a brighter nacre and a less dark epidermis. In the specimens before me 

 the nacre is much worn and the substance of the shell eroded. The beaks are so 

 much eroded that there are no remains of divergent folds with which they were no 

 doubt once clothed. It is nearly allied to Paraguayensis, herein described, but differs 

 much in the elliptical outline. 



Unio ampullaceus. pi. 35, fig. 83. 



Testa Irevi, suboblonga, valde inflata, iniequilaterali, postice obtuse angulata, antice rotuudata ; 

 valvuli.s crasslusculis, antice crassioribus ; natibus subprominentibus, iuflatis ; epidermide 

 tenebroso-fusca, rugoso-striata, eradiata; dentibus cardinalibus parvis, obliquis, lamellatis, iu 

 ^ utroque valvule duplicibus; lateralibus longis, subrectis, lamellatis corrugatisque ; marganta 

 alba et iridescente. 

 Shell smooth, oblong, very much inflated, inequilateral, obtusely angular behind 

 and rounded before; valves somewhat thick, thicker before; beaks prominent and 

 inflated ; epidermis dark brown, rugosely striate and without rays ; cardinal teeth 

 small, oblique, lamellar and double in both valves; lateral teeth long, nearly straight, 

 lamellar and corrugate ; nacre white and iridescent, 

 Proc. Acad. Nat. Sci. 1866, p. 34. 

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

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

 Diara. 1-1, Length 1-5, Breadth 2-5 inches. 



Shell smooth, oblong, very much inflated, inequilateral, obtusely angular behind 

 and rounded before ; substance of the shell somewhat thick, thicker before ; beaks 

 prominent and inflated; ligament rather small and dark brown; epidermis dark 

 brown, rugosely striate, without rays and with rather distant marks of growth ; 

 umbonial slope rounded and much inflated ; posterior slope elliptical, somewhat cari- 

 nate, rather wide, very dark brown and with an impressed line in each valve ; 

 cardinal teeth small, oblique, lamellar and double in both valves ; lateral teeth long, 

 nearly straight, lamellar and corrugate; anterior cicatrices confluent, rather large 

 and well impressed; posterior cicatrices confluent and slightly impressed; dorsal 

 cicatrices placed across the cavity of the beaks; cavity of the shell deep and 

 rounded ; cavity of the beaks very shallow and rounded ; nacre white and iridescent. 

 Remarks.— k. single specimen only of this species was received. The beaks are 

 much eroded, but still an indistinct indication remains of the divergent character of 

 the tips. In outline it is closely allied to Mexicanus, Pliili., but diflers entirely iu the 

 teeth and the color of the nacre. It is also very near to Charnaunis, D'Orb , but is 

 more inflated and not so wide. It reminds one o^ -DlatuUn'/uium (nobis), but is more 

 quadrate than that shell and less oblique. In the speciuien before me there are 

 sliglitly impressed lines running from the beaks to tlie anterior hulf of the margin 



