. PART I. 

 AQUATIC. 



CLASS I. CONCHIFERA, OR BIVALVES. 

 Order. LAMELLIBKANCHIATA (with leaflike cfills). 

 Family I. SPH^ERIDJE. 

 Genus L 



1. S. COENEUM (horn- colour ed) . 



Shape somewhat globular ; thin, glossy, opaque, yellow- 

 ish horn-colour, with bands of a paler tint indicating the 

 lines of growth, striated finely and evenly in the same 

 direction, also faintly striated from the beaks to the 

 margin ; ligament short ; hinge furnished with a double 

 cardinal tooth in each valve two lateral teeth in the right, 

 and four in the left valve ; muscular scars faint. 



This common shell is found at the roots of weeds, 

 and in the mud in ponds, ditches, canals, and rivers in 

 every part of the British Isles. 



It varies considerably as follows : 



Var. I. flavescens. Smaller, more globular, and 

 paler. 



Var. II. nucleus. Smaller, nearly spherical. 



