SUPPLEMENT TO ISAAC LEA'S PAPER ON UNI0NIDJ3. 65 



shallow and wide ; cavity of the beaks shallow and rounded; nacre livid color and 



very iridescent. 



Remarks.— Quite a number of specimens have been in my possession for some 

 time. Recently I have compared them with their allied species and am now satis- 

 fied the species is distinct from any described. It is very near in outline to errans 

 (nobis), but it is not so stout. It is also allied to Hallenheckii (nobis), but that 

 species is much more ponderous and is of a darker epidermis. 



Unio Gesnerii. pi. 22, fig. 61. 



Testa tevi, suboblonga, inflata, insequilaterali, postice subbiangulari, antice oblique rotnndata ; val- 

 vulis subcrassis, antice crassioribus ; natibus prominulis ; epidermide teijebroso-fusca, vel radiata 

 vel eradiata; dentibus cardinalibus crassiiiseulis, in utroque valvulo subduplicibus sulcatisque ; 

 lateralibus longis, crassis lamellatisque ; niargarita livida et iridescente. 



Shell smooth, suboblong, inflated, inequilateral, subbiangular behind, obliquely 

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

 epidermis dark brown, radiated or not radiated; cardinal teeth somewhat thick and 

 somewhat double in both valves; lateral teeth long, thick and lamellar; nacre 



livid color and iridescent. 



Proc. Acad. Nat. Sci., 1873, p'. 424. 



Hah.— \5c\ieQ River, near Columbus, Georgia, Dr. W. Gesner and Bishop Elliott. 



My cabinet and cabinet of Dr. Lewis. 

 Diam. -9, Length 1-6, Breadth SI inches. 



Shell smooth, oblong, somewhat compressed, very inequilateral, subbiangular 

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

 somewhat prominent ; ligament moderately thick and dark brown; epidermis dark 

 brown, obscurely rayed, with rather distant marks of growth; umbonial slope 

 rounded; posterior slope narrow elliptical; cardinal teeth rather small and sulcate, 

 and somewhat double in both valves; lateral teeth long, thick and lamellar; ante- 

 rior cicatrices distinct, rather large and well impressed ; posterior cicatrices conflu- 

 ent, well impressed and large; dorsal cicatrices above the centre of the cavity of 

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

 shallow and rounded ; nacre livid color and iridescent. 



Remarks. — Eight specimens of various ages were sent to me by Dr. Lewis, who 

 received them from Dr. Gesner, and I am glad to name the species in honor of him. 

 One specimen came from Bishop Elliott. In outline it is near to Chathamensis (nobis) 

 and reminds one of errans (nobis), but it may easily be distinguished from them. 

 The younger specimens all have close, fine rays over the whole disk. The undula- 



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