32 DESCRIPTIONS OF 



cicatrices placed in the centre of the cavity of the beaks; pallial cicatrix well 

 impressed ; cavity of the shell rather deep and rounded ; cavity of the beak somewhat 

 deep and subangular ; nacre purple or rose color and very iridescent. 



Remarks. — When I described Unio Tampicoensis, in 1835, (Trans. Am. Phil. Soc. 

 Vol. 6, p. 24,) I was in possession of the above described shell also by the kindness 

 of the late Dr. Burrough. In the remarks, I then mentioned that in the younger 

 specimens the epidermis was of a yellow brown, and that indistinct rays might be 

 observed. Having had access to other specimens all of the same size, and particularly 

 a fine one from Mr. Anthony, of Cincinnati, who also obtained it from Dr. Burrough's 

 collection, I am satisfied that, although nearly allied to Tampicoemis, it must be 

 considered to be distinct. It differs in being not quite so oblique, in the beaks not 

 being so prominent, the epidermis not being blackish but of a fine dark brown. It 

 also has obsolete rays, while the other seems to have none, and the nacre is disposed 

 to be more rose color and purple. All the specimens before me are more or less thus 

 colored, while Tampicoensis, is usually white with pinkish lateral teeth. 



There is rather a remarkable feature in the three specimens before me, about the 

 centre of the cavity of the interior of the disk, all of which are granulose with small 

 irregular pearls. 



Unio Newcombianus. PI. 30, fig. 27. 



Testa corrugato-sulcata, rotundata, subcompressa, insequilaterali ; valvulis crasis ; natibus elevatis piominen- 



tibusquc ; epidermide tenebroso-olivacea, corrugata ; dentibus cardinalibus submagnis, duplicibus sub- 



compressisque ; lateralibus subbrevlbus, crassis subcurvisque ; margarita alba. 



Shell corrugately sulcate, rounded, somewhat compressed, inequilateral ; valve thick ; 



beaks elevated and somewhat prominent ; epidermis dark olive, corrugate ; cardinal 



teeth rather large, double and somewhat compressed ; lateral teeth rather short, thick 



and somewhat curved ; nacre white. 



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



Hah. — Nicaragua. W. Newcomb, M. D. 



My cabinet and cabinets of Dr. Newcomb, Albany, and C. M. Wheatley, New York. 

 Diam. -6, Length 1-1, Breadth 1-3 inch. 



Shell roughly furrowed, rounded, somewhat inflated over the umbones and flattened 

 towards the basal margin, inequilateral ; substance of the shell thick, thinner behind ; 

 beaks elevated, somewhat prominent and subangular ; furrows transverse and roughly 

 wrinkled, rather close and covering the whole disk ; ligament very short and not very 

 thick; epidermis dark olive and roughly wrinkled; umbonial slope obtusely angular; 

 cai'dinal teeth rather large, somewhat compressed, double in both valves ; lateral teeth 

 single in the right and double in the left valve ; rather short, thick and somewhat 

 curved, in the left valve the inferior division being clavate, the superior very small and 



