Parr’ I, 
BO AP TG: 
Crass I—CONCHIFERA, OR BIVALVES. 
Order—LAMELLIBRANCHIATA (with leaflike gills). 
Family .L—SPHARIDA. 
Genus I.—SPHERIUM. 
1. S. corneum (horn-coloured). 
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. 
