New Species of Unio froni fhf Rh'er Glenchj. 113 



posterior dorsal keel steep, broad, triangular, conspicuous 

 externally, and visible internally. Unibones prominent, deeply 

 eroded in adult shells. 



Surface rough with two series of markings, one consisting 

 of undulating concentric ridges, a few of which are coarsely 

 crenulated, and the other of five or six rows of irregular, pro- 

 minent, nodose wrinkles angularly arranged around the umbo 

 and with deeply-cut interspaces. The latter series of markings 

 is oblique to the former and constitutes a characteristic rib- 

 like ornament. 



Epidermis thick, brown to brownish black. Internal sur- 

 face smooth in adult shells, nacre bluish to light brown, not 

 brilliant. 



Cardinal teeth faintly indicated, anterior in left and lower 

 anterior in I'ight frilled, and with a deep pit beneath them in 

 both valves. 



Length -40, breadth 23, thickness through both valves 13-5 

 millimetres. 



The species is allied to U. depressus by its dentition, but 

 differs from that shell in shape as well as in other important 

 features. U. nepeanoisis shews a few wrinkles on the umbonal 

 region, but as far as I can judge by the single example in 

 my collection its surface is otherwise comparatively smooth, 

 while in general outline it resembles young examples of U. 

 aiistralis. 



