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ART. XIII. — New Unionidce of the United States and Northern Mexico. 



By Isaac Lea, LL. D. 



Since the publication of my exotic paper in the last part of the Academy's Journal, 

 I have procured many new indigenous species, and a few from Northern Mexico. I 

 now return to them, having made full descriptions of their outward forms ; and 

 when I had the advantage of having the soft parts, I have carefully made examina- 

 tion of them and given their characters. It is to be regretted, however, that the 

 living animals can rarely be obtained of new species. The drawings will be found to 

 be made with great care and their natural characters carefully preserved. 



TJnio dispar. PI. 51, fig. 153. 



Testa laevi, elliptica, subinflata, ad latere paulisper planulata, valde intequilaterali, postice" obtuse angulata, 

 antice rotundata ; valvulis subcrassis ; natibus prominulis, ad apices undulatis ; epidermide vel lutea 

 vel oliva et valde radiata ; dentibus cardinalibus parviusculis, compressis, erectis, erenulatis, in utroque 

 valvule- duplicibus ; lateralibus longis, lamellatis curvisque ; margarita alba et iridescente. 



Shell smooth, elliptical, somewhat inflated, a little flattened at the sides, very ine- 

 quilateral, obtusely angular behind and rounded before ; valves rather thick ; beaks 

 a little prominent and undulate at the tips ; epidermis yellow or olive and very much 

 rayed ; cardinal teeth rather small, compressed, erect, crenulate and double in both 

 valves ; lateral teeth long, lamellar and curved ; nacre white and iridescent. 

 Proc. Acad. Nat. Sci. 1860, p. 305. 



Sab. — Columbus, Georgia. Bishop Elliott and G. Hallenbeck. 



My cabinet and cabinets of Bishop Elliott and G. Hallenbeck. 

 Diam. -7, Length 1-2, Breadth 2*2 inches. 



Shell smooth, elliptical, somewhat inflated, a little flattened at the sides, very ine- 

 quilateral, obtusely angular behind and rounded before ; substance of the shell rather 

 thick ; beaks a little prominent, with numerous small undulations at the tips ; liga- 

 ment rather short, thin and light brown ; epidermis yellow, varying to olive, radiated 

 all over the disk, but most strongly on the posterior portion ; umbonial slope slightly 

 raised and rounded ; posterior slope somewhat carinate, and covered with dark green 

 rays ; cardinal teeth rather small, compressed, erect, crenulate and double in both 

 valves ; lateral teeth long, lamellar and curved ; anterior cicatrices distinct and. well 

 impressed; posterior cicatrices confluent and slightly impressed ; dorsal cicatrices 

 placed nearly in the centre of the cavity of the beaks ; cavity of the shell rather 

 shallow and wide ; cavity of the beaks shallow and subangular ; nacre white and 

 very iridescent. 



