FRESH WATER AND LAND SHELLS. 255 



trices nearly in the centre of the cavity of the beaks, on the inferior posterior part of the 

 cardinal tooth; pallcal cicatrices distinctly impressed; cavity of the shell shallow, cavity 

 of the beaks shallow and subangular; nacre white and iridescent. 



Remarks. — It is to be particularly regretted that a single specimen only of this species 

 should have been received from Dr. Gibbes. The cardinal teeth in both valves arc tripartite. 

 They are distinctly divided into three lobes, of nearly equal size and form. This is so unique 

 that I have inserted it with some hesitation as a permanent character, tripartition being 

 so unprecedented. It may possibly be accidental. Should other specimens prove this 

 form to be persistent, this species will present an anomaly peculiarly its own. The lateral 

 teeth are, as usual, single in the right and double in the left valve; but the terminal in- 

 ferior portion is remarkably enlarged and thickened in the latter valve, so as to run 

 beyond the superior portion. The marginal portion of the disc is remarkably furnished 

 with imbricate epidermal matter. It has somewhat the outline of U. complanaius, but may 

 easily be distinguished from that species by its being more elevated in the beaks, in its 

 imbricate margin, and in the form of the teeth. 



UnIO PERSTR1ATUS. PI. XII. Fig. 3. 



Testa Isevi, valde transversa, valde compressd, subemarginatd, valde insequilaterali, postici subbiangidata; 

 valvalis lenitibus ; nalibus parvis,vix prominent ibus, ad apicem undulalus ; epidermide luleo-fuscd,perstriald$ 

 denlibus cardinalibus parvis, obliquis; lateralibus prxlongis rectisqitc; margaritd alba el iridescente. 



Shell smooth, very transverse, very much compressed, subemarginate, very inequilateral, subbiangular behind; 

 valves thin; beaks small, scarcely prominent, undulated at the tip; epidermis yellowish-brown, very much 

 striated; cardinal teeth small, oblique; lateral teeth very long and straight; nacre white and iridescent. 



Hab. Abbeville District, S. C. J. P. Barratt, M. D. 

 My cabinet and cabinet of Dr. Barratt. 

 Diam. .5, Length 1, Breadth 2.3 inches. 



Shell smooth, very transverse, very much compressed, slightly emaiginate, very inequi- 

 lateral, subbiangular behind, obtusely rounded before, posterior slope wide and flattened; 

 substance of the shell thin; beaks placed near to the anterior margin and furnished with 

 minute undulations at the tip, scarcely prominent, but rather pointed; ligament long and 

 thin; epidermis yellowish-brown, with numerous imbricate stria; covering nearly the 

 whole of the disks, rind with only one or two distant marks of growth; utnbonial slope 

 biangular and flattened; cardinal teeth small, oblique, double in the right and single in 

 the left valve; lateral teeth very long, straight and thickened at the posterior ends; 

 anterior cicatrices distinct; dorsal cicatrices placed under the plate between the cardinal 

 and lateral teeth; cavity of the shell exceedingly shallow; cavity of the beaks very shal- 

 low and rounded; nacre white and iridescent. 



Remarks. — Dr. Barratt sent me four specimens of this species, which may easily be 

 distinguished by its peculiar striated epidermis, and its compressed form. It scarcely 

 belongs to that large groop of which the V.complanatus is the type, hut certainly borders 



on it. The nacre of three of the specimens is white, slightly tinged with blue. The 

 fourth specimen is purplish. The lines of growth arc very remarkable, being low and 



