CHIEFLY OF THE UNITED STATES. 2(33 



snjall, oblique, lamellar, single in the left and double in the right valve; lateral 

 teeth long, lamellar and nearly straight; anterior cicatrices confluent and slightly 

 impressed ; posterior cicatrices confluent and very slightly impressed ; dorsal 

 -cicatrices j^laced in the centre of the cavity of the beaks ; cavity of the shell wide 

 and somewhat deep; cavity of the beaks shallow and subangular ; nacre bluish-white 

 and iridescent. 



Soft Parts. — A single dried specimen only was received. It was so poor that I was 

 only enabled to make out the ova in the ovarium and in the branchial uterus. These 

 ova were not sufficiently advanced to make out the embryonic form perfectly, but 

 they were enough so as to show that it was pouch-shape. The branchial opening 

 was mutilated as well as the palpi and the papillae. 



Remarks. — A single specimen only is before me. It is a small species, and this 

 individual is about an inch wide. It probably is not quite grown. In outline it is 

 near to elUpticum, Spix, but is more nearly allied to inoraatus (nobis). It cannot be 

 confounded with either. The epidermis is of a brilliant polish, and the single band 

 of growth is distinctly marked by a dark and yellow line. The cardinal tooth, being- 

 double in the right and single in the left valve, is of an unusual character. 



Unio apprimus. pi. 3-3, fig. 7S. 



« 



Testa Ifevi, elliptica, inflata, insequilaterali, postice emargiuata, obtuse angulata, antice rotundata ; 

 valvulis percrassis, antice crassioribus ; uatlbus subpromluentibus, ad apices divaricate uudulatis ; 

 eplderniide castauea, micanti, substriata, obsolete radiata ; dentibus eardinalibus grandibus et 

 valde partitis ; lateralibus prselongis, lamellatis, curvatis et decore granulatis ; mai'garita argentea 



et iridescente. 



Shell smooth, elliptical, inflated, inequilateral, obtusely angular and emarginate 

 behind and rounded before ; valves very thick, thicker before ; beaks rather 

 prominent, with divergent folds at the tips; epidermis chestnut-brown, shining, 

 somewhat striate and obscurely rayed; cardinal teeth large and very much divided; 

 lateral teeth very long, lamellar, curved and beautifully granulate ; nacre silver- 

 white and very iridescent. 



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



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



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

 Diam. VI, Length 2-6, Breadth 39 inches. 



Shell smooth, elliptical, inflated, inequilateral, obtusely angular and emarginate 

 behind and rounded before ; substance of the shell very thick, thicker before ; 

 beaks rather prominent, with divergent folds at the tips; ligament large and light 

 thrown ; epidermis chestnut-brown, shining, somewhat striate, obscurely rayed, with dis- 



