British Species of My til us. 



87 



wards, and forming an angle with the forepart of the shell. In 

 M. cygneus the base slopes upwards ; and the M. incrassatus dif- 

 fers from them all by its large exserted ligament, superior rough- 

 ness on the outside, and in having the posterior part in a slope 

 from the umbones to the base incrassated. 



I am, <xc. 



Wrabness Parsonage, Essex, 

 Dec. 18, 1819- 



Revett Sheppard. 



4 



XL Otoer- 



