C 295 ] 



ART. XXVIII. — Descriptions of New Species of Unio. 

 By T. a. Conrad. 



U. Aberti. pi. 26, fig. 1. — Saboval, much compressed, contracted from beak to base; posterior margia 

 truncated, direct; basal margin contracted posteriorly ; beaks submedial ; umbonal slope prominent or 

 ridged, rounded ; middle of disk with irregular plicas running from umbo to base, becoming obsolete at 

 base; posterior slope with wrinkled lines and small plicae; epidermis olive-jcllow, with small, very 

 numerous green dots, and a few broad rather indistinct rays ; within pale pink; cardinal teeth thick, 

 direct. 



v. Aherti, Con. Proceed. Ac. Nat. Sc. v. p. 10, 1850. 



U. Lamarhianus, Lea. Trans. Amer. Philos. Soc, 2d series, x. pi. 17, fig. 20, 1852. 



Locality. Chambers' Ford, rapids of Verdigris river, Arkansas. Dr. Woodhouse, 



Dedicated to Col. J. J. Abert. 



This beautiful shell probably belongs to the sub-genus Theliderma, Swain.son, 

 The tubercles are small and obsolete. Its affinity is probably with U. intermedins, 

 Con. 



U. DEPRESSUS, Lam. PI. 26, fig. 2. 



U. cullelliformus, Con. Proceed. Acad. Nat, Sci., v. p. 10. 



Locality. Began river, Australia. 



The shell I have described appears to be the adult, or a large variety of Lamarck's 

 species. The figure represents the latter, copied from Delessert's plate. It resembles, 

 in outline, U. arctatus, Con., but may be readily distinguished from any American 

 species of similar form, by the long compressed cardinal teeth, as represented in 

 Delessert's figure, which also exhibits the third muscular impression, situated at the 

 anterior base of the cardinal teeth, a character which widely removes it from the 

 North American species. 



U. Balonnensis. PI. 26, fig. 3. — Suboval, or somewhat trapezoidal ; disk contracted from beak to base ; 

 posterior side inflated ; posterior margin obliquely truncated, extremity acutely rounded and much above 

 the line of the base ; ligament and basal margins parallel ; basal margin nearly straight in the middle; 

 umbonal slope rounded ; posterior submargin with transverse wrinkled lines ; epidermis olivaceous, 

 strongly lined concentrically ; within white ; lateral teeth compressed; cardinal teeth elongated, com-, 

 pressed, very oblique, single, or slightly disposed to be double iu each valve. 



This very distinct and well characterized species has been referred by Lea to 

 v. depressa, Lam. This is an oversight. Probably he intended Napeanensis, when 

 he wrote Balonneiisis, for there is no resemblance between the latter ventricose shell 

 and depressa, and all three are widely diiTeront. 



