25 



and one-eigblli, and its width, in the most ventricose 

 part, half an inch. 



The form of the shell is nearly intermediate between 

 Unio pictorum and Unio margavitiferus. 



In all probability other similar specimens will be 

 found in the same locality, and, in this case, a drawing 

 and further description will be given at the conclusion 

 of the work. 



Anodonta. 



This very interesting branch of the family have 

 usually a much thinner and more fragile shell than the 

 Unios. The shell is equivalvc, the ligament is external, 

 and the hinge contains no teeth. 



The form of the Anodonta must be looked upon as 

 the most varied of the British mollusca, and in size 

 also it differs very considerably. 



Professor Forbes remarks, in his new work, that in 

 spring and summer the branchial leaflets of the female 

 are filled with minute yet complete shelled young ones, 

 to the number of many thousands. 



. Anodonta cygnea (Swan Fresh-water Muscle). 



Linnaus. 



Figure II. 



