NEW FRESH WATER AND LAND SHELLS. 33 



thin ; anterior cicatrices distinct and deeply impressed ; posterior cicatrices confluent 

 and rather deeply impressed ; dorsal cicatrices numerous and placed within the cavity 

 of the beaks ; pallial cicatrix distinctly impressed ; cavity of the shell rather shallow 

 and regularly rounded ; cavity of the beaks rather deep and angular ; nacre white. 



Remarks.— Among the Unimesoi Lake Nicaragua, this species, taken by Dr. New- 

 comb, has not, I believe, heretofore been observed. It is a very remarkable species, as 

 well from its outline, as from its singular corrugate and furrowed disk. It differs from 

 all the species which I know, in this character. We have some species of Naiades 

 with wrinkled epidermis,* but not so much so as this, nor are they accompanied by 

 furrows like this. It differs from U. araiiis, (nobis,) also from Lake Nicaragua, in 

 beino- round and in having wrinkles as well as furrows. Two of the three specimens 

 before me are adult, and in these there is apparently, in the left valve, a disposition 

 to form a third division of tooth. The largest of the three specimens is probably a 

 female, as there is an enlargement at the posterior basal margin, which indicates that 

 sex. It causes the outline to present a subtriangular form, which is not the case with 

 the other two. 



I owe to Dr. Newcomb the possession of this beautiful little species, as well as many 

 other fresh water and land shells, and with pleasure dedicate it to him, who has proved 

 so industrious and successful an investigator in this branch of Zoology. 



Unio cambodiensis. pi. 30, fig. 28. 



Testa Isevi, elliptica, subinflata, iDrequilaterali ; valvulis subtenuibus ; natibus protninentibus, ad apiceiu 

 undulatis ; epidermide castanea, eradiata, polita ; dcntibus cardinalibus longis, rectis lamellatisquc ; 

 lateralibus sublongis, lamellatis subrectisquc ; margarita alba et iridescente. 



Shell smooth, elliptical, rather inflated, inequilateral ; valves rather thin ; beaks a 

 little prominent, undulated at the tip ; epidermis chestnut colored, without rays and 

 polished ; cardinal teeth long, straight and lamellar; lateral teeth rather long, lamellar 

 and nearly straight ; nacre white and iridescent. 

 Proc. Acad. Nat. Sci. Vol. 8, p. 103. 



jjab. — Tackrong River at Korat, Cambodia. S. R. House, M. D. 

 Cabinet of Mr. W. A. Haines. 

 Diam. -4, Length -5, Breadth 1 inch. 



Shell smooth, elliptical, rather inflated, inequilateral, sub-biangular behind ; 

 substance of the shell thin ; beaks a little prominent and subinflated, undulated at 

 the tip ; epidermis chestnut color disposed to rufous, without rays, shining ; ligament 

 very short and thin ; umbonial slope obtusely angular ; posterior slope carinate, with 

 two raised lines running from the beak to the posterior basal margin, nearly covered 

 with minute folds ; cardinal teeth long, straight, lamellar, single in the k/t and double 



*Anadunta cri.tjHihi, Lam., from Cayenne, and An. lurlilis, (nobis,) from Carthagcna. 



9 



