104 



oblique lines; beaks not prominent, eroded; basal 

 margin nearly straight; posterior extremity truncat- 

 ed, direct; epidermis olivaceous, with crowded pro- 

 minent wrinkles, and with rather indistinct green 

 rays; within bluish or purplish; cardinal teeth com- 

 pressed, oblique. 



OBSERVATIONS. 



Some specimens of this shell might be readily mis- 

 taken, without close examination, for U. complanatus, 

 but the species is more nearly allied to U. congarceus. 

 It differs in having a more elevated ligament margin, 

 an inflated umbonial slope, and is proportionably 

 longer. It is a very abundant species in the Black 

 Water river, Virginia, and occurs also in the Neuse 

 river, North Carolina, where it always has a very 

 rough wrinkled epidermis, of a dark colour. The 

 figure is from a specimen found by Dr. Blanding in 

 the Yadkin river, North Carolina, where it is more 

 narrowed posteriorly, smoother, thicker, and has a 

 lighter coloured epidermis than those from the Black 

 Water and Neuse rivers. One specimen is quite 

 thick and salmon coloured within. 



UNIO METASTRIATUS. 



Plate LVIL— Fig. 2. 



DESCRIPTION. 



Shell subtriangular, moderately thick; umbo and 

 disk flattened, but forming a strongly arcuate line 



