UNIO. 13 



the surface being generally painted more or less dis- 

 tinctly with rays of colour, varying from brown to a 

 bright green or yellow; occasionally they are met with 

 of a uniform brown, or purplish tinge. They vary 

 from two and a half to three inches in length, by about 

 an inch and a half in the broadest part. 



Hob. Found abundantly in some of the streams in 

 the south of Lancashire and Yorkshire; it has also been 

 found in the New River, Avon, Kennet, Ouse, &c. 



U. PICTORUM. Linnceus. PI. Ill, fig. 1. 



Oval, oblong, posterior end not cuneiform ; of a yellowish green colour 

 interspersed with brownish zones; anterior teeth, compressed, elevated, 

 crenate. 



Mya pictorum. Linn. Unio rostrata. Lam. 



One of the distinguishing peculiarities of this Unio is 

 that its dorsal and ventral margins run almost parallel. 

 The rays of colour also generally so conspicuous in U. 

 tumidus are wanting here. Internally it is white, or 

 approaching salmon colour. It frequently attains a 

 greater length than U. tumidus ; breadth about the 

 same. 



Hob. The recorded localities are numerous, Ken- 

 net, Avon, several of the Yorkshire rivers, Severn, and 

 almost all canals having a muddy bottom ; it has not 

 been found further north than "Winyard. 



U. Batavus, and U. ovalis we have rejected, the 

 former appears to be foreign, and the latter only a dis- 

 torted form of U. tumidus. 



U. MARGARITIFEK.US. LiuHCBUS. PL I, fig. 1. 



Ovate, oblong, thick, solid; epidermis brownish black; cardinal 

 teeth, thick, conical; no lateral teeth. 



Mya margaritifera, Linn, Retz., fyc. Alasmodon 

 magaritifera, Gray. 



This is the shell which obtained so much celebrity 

 amongst the ancients on account of the pearls which are 

 sometimes found in the body of the animal. These 

 pearls seem to be malformations, and are generally 

 formed between the two films or skins that line the 



