AND DESCRIPTIONS OF NEW SPECIES. 85 



substance of the shell very thick ; beaks nearly terminal and very 

 much elevated ; ligament rather short and thick; epidermis blackish 

 brown, behind the beaks on the second growth it is yellow; tip of the 

 beaks yellowish ; cardinal teeth large and oblique, being in a line 

 nearly parallel to the lateral tooth which is thick and slightly curved ; 

 posterior and anterior cicatrices both distinct ; dorsal cicatrices situated 

 on the under side of the plate between the cardinal and lateral 

 teeth ; cavity of ihe beaks deep and angulated ; nacre pearly white and 

 iridescent. 



Remarks. — This species, which seems to be peculiar in the yellow 

 mark behind the beaks, resembles the- U. mytiloides- (Rafin.) and 

 might easily be mistaken for a ventricose variety of that species where 

 the beaks are so much eroded as to have destroyed the second growth. 

 A young individual of second growth is represented in the plate to ex- 

 hibit the curious distribution of colour. The posterior third is yellow 

 and the remainder green, the line of separation being very distinct. 

 Those of three growths usually have no trace of yellow on the third 

 growth which takes a brown colour. The first growth, which may 

 be considered the tip of the beaks, is usually yellow or yellowish 

 green over its whole surface. The largest specimen given in the 

 plate is not more than one fourth the size it is sometimes found. It 

 is selected, because it is the Largest I have seen with the beaks suffi- 

 ciently perfect to exhibit the peculiar yellow colour of this part. 



Unio Asper. Plate IX. fig, 15. 



Testa subtriangulari, inaquilaterali, postice angulata, valde tuberculatd ; valvulis 

 crassis; dentibus cardinalibus subgrandibus ; lateralibus aliquantulum curvatis ; 

 margaritd alba. 



Shell subtriangular, inequilateral, angular behind, much tuberculated; valves 

 thick; cardinal teeth rather large; lateral teeth slightly curved; nacre pearly white. 



Hab. Alabama river, Judge Tait. 

 Vol. IV.— W 



