21 



ing epidermis is in some degree olive, interspersed with 

 transverse greenish rays, which converge to a point 

 towards the umbones. Sometimes the shell is entirely 

 free of these transverse markings, and other specimens 

 are of a uniform pale brown colour. The ligament is 

 large, shining, and projects. The inside of the valves 

 is mostly of a blueish-vthite colour; occasionally speci- 

 mens are found which are salmon-coloured, but they 

 are of rare occurrence, excepting in the canal near 

 Beeston, where the proportion is two in five. The 

 primary teeth have much strength and are slightly com- 

 pressed ; the hinder teeth on the left valve are upright, 

 being almost perpendicular. 



In speaking of a fine specimen, Professor Forbes re- 

 marks, it measures 3 inches in length, and rather more 

 than 1 1 inches in breadth in the widest part. Larger 

 specimens have been taken from the river Trent, near 

 Beeston. One I have lately obtained is rather more 

 than 3 J inches long, by slightly more than 1| inches 

 broad, 



Unio tumidus is more solid than Unio pictorum, and 

 is furnished with larger and stronger anterior teeth. 

 The shell tapers behind, and is broader than Unio 

 pictorum. 



It inhabits slow rivers and canals, and appears to 

 grow more vigorously in the former than in the latter 

 localities. 



It may be considered, in this ueighbourhood, to be an 

 abundant shell, in the localities where it is found, and 

 these are, the river Soar at Thrumpton, the river Trent 

 from Sawley to Beeston, and the canal at Beeston. 



More distant recorded localities are, the New River, 

 the river Avon, the river Kennet, and the river Ouse 

 (Forbes and Hanley), Ely River, Cardiff (Jeffreys), 

 near London (Grey), Newcastle (Alder), Germany 



