CHIEFLY OF THE UNITED STATES. 289 



angular behind, round before; valves rather thin; beaks slightly prominent; 

 epidermis yellowish or green rayed ; nacre bluish-white and very iridescent. 

 Proc. Acad. Nat. Sci. 1868, p. 96. 



Hob. — Lake Nicaragua, Central America, Col. E. Jewett. 



My cabinet and cabinets of Col. Jewett and Academy of Natural Sciences. 

 Diam. -6, Length -9, Breadth 1-4 inch. 



Shell smooth, elliptical, somewhat inflated, ineqiiivalve, inequilateral, obtusely 

 angular behind, round before ; substance of the shell rather thin ; beaks slightly 

 prominent ; ligament thin and short ; epidermis yellowish or green rayed ; umbonial 

 slope rounded ; posterior slope carinate, elongate elliptical ; anterior cicatrices con- 

 fluent and but little impressed; posterior cicatrices confluent and very slightly 

 impressed ; dorsal cicatrices placed in the upper part of the cavity of the beaks ; 

 cavity of the shell shallow ; cavity of the beaks very shallow ; nacre bluish-white 

 and very iridescent. 



Remarlts. — .This species is allied to leniicularis and incequivalva, herein described, 

 but may be distinguished by being more transverse than either. The three are very 

 closely allied, but I think they cannot belong to one species. I have been impressed 

 by the fact that, in the Unlonidoe of Lake Nicaragua, the specific differences are so 

 small that one cannot, with entire satisfaction, seize well defined and characteristic 

 differences, while it is evident they exist. 



Anodonta Jewettii PL 41, fig. 101. 



Testa Irevi, suboblonga, valde inflata, parum incequilaterali, postice rotundata, antice oblique rotun- 

 data ; valvulis tenuibus ; natibus prominentibus, iuflatis ; epidermide olivacea, transverse striata, 

 fere sulcata, obsolete radiata ; margarita argentea et valde iridescente. 



Shell smooth, suboblong, very much inflated, somewhat inequilateral, rounded 

 behind and obliquely rounded before ; valves thin ; beaks prominent, inflated ; 

 ej)idermis olivaceous, transversely striate, almost sulcate and obscurely radiate ; 

 nacre silver-white and very iridescent. 



Proc. Acad. Nat. Sci. 1868, p. 95. 



iDg list will, I hope, induce more attention to the investigation, by students of Fresh-water Molluscs, of this 

 interesting branch of inquiry : 



List of ineqiiivalve Unionidce. 



Triquetra contorta, China. Unio encarpus, Central America. 



Spatha Natalensis, Africa. Unio Nicaraguensis, Central America. 



Unio tortuosus, China. Anodonta inicquivalva, Central America. 



Unio Newcombianus, Central America. Anodonta Granadensis, Central America. 



Unio Gabbianug, Central America, Anodonta lenticularis. Central America." 



Pro. Acad. yaf. Sci., March, 1868. 



