NEW FKESil WATER AND LAND SHELLS. 29 



cardinal teeth large, somewhat thick, double in both valves, crenulate ; lateral teeth 

 long, thick and slightly curved; the two inferior anterior cicatrices confluent, the 

 superior one being distinct; posterior cicatrices confluent; dorsal cicatrices placed 

 across the centre of the cavity of the beaks ; cavity of the shell rather deep ; cavity 

 of the beaks shallow ; nacre white or flesh color and iridescent. 



Remarlcs. — A young shell, apparently not one-fourth grown, was sent tome some time 

 since by Mr. C. M. Wheatley, who procured it from the Rio Negro, at the distance of 

 1200 miles from the mouth of the Amazon. After comparing this young individual 

 carefully with all my South American specimens, and with the desci'iptions of Spix 

 and Von Martins, as well as those of D'Orbigny, I am satisfied that it can only be as- 

 similated to a specimen which that distinguished traveller and zoologist, Mr. D'Orbigny, 

 sent to me with several other specimens as U. lacteohis, (nobis,) {delodontus, Lam.) I 

 have always doubted that specimen being the same species with those which it accom- 

 panied, and now connect it with this young specimen under the name of my friend 

 Mr. Wheatley. I am not prepared to say, when we shall find mature specimens from the 

 Rio Negro, that it may not prove distinct from the shell from Monte Video. The form 

 of the former is more triangular, and it varies in being flesh colored. The species above 

 described may be distinguished from delodontm, Lam., by being less transverse, and 

 having longer and larger diverging ribs at the beaks, which in both specimens before 

 me converge a short distance below the tip of the beak so as to form re-entering 

 angles. It differs from Burroughiann-s, (nobis,) and Paranensis, (nobis,) in being less 

 transverse than the former, and being less rotund than the latter. It is also less 

 rotund than memhranacetis, Matou. 



Unio suavidicus. pi. 29, fig. 24. 



Testa laevi, oblonga, sabcompressa, valde inEequilaterali, antic6 rotundata, posticetruncatii; natibus subpronii- 

 nentibus, costis elevatis; epidermideluteo-sliva, minute striata ; dentibus'cardinalibus parvis, compressis, 

 crenulatis in utroque valvulo duplicibusque; lateralibus longis, lamellatis subrectisque ; margarita 

 cxruleo-alba et iridescente. 



Shell smooth, oblong, somewhat compressed, very inequilateral, rounded before and 

 truncate behind ; beaks a little prominent, with elevated ribs ; epidermis yellowish 

 olive, minutely striate ; cardinal teeth small, compressed, crenulate and double in both 

 valves; lateral teeth long, lamellar and nearly straight; nacre bluish white and 

 iridescent. 



Proc. Acad. Nat. Sci. Vol. 8, p. 95. 

 Hah. — River Amazon. Mr. E. Verreaux, Paris. 

 My cabinet. 

 Diam. 4, Length 0, Breadth -8 inch. 



Shell smooth, oblong, somewhat compressed, very inequilateral, rounded before and 

 truncate behind, dorsal and basal lines nearly parallel ; swollen before the umbonial 



