DESCRIPTIONS OF THE 
SPECIES AND VARIETIES OF 
BRITISH LAND AND FRESH- 
WATER SHELIS. 
SPHZRIUM CORNEUM. LINN. 
SHELL suborbicular, or rounded-ovate, equilateral, with 
fine concentric striations, brownish, or yellowish-brown ; 
umbones broad and blunt, and nearly central in position ; 
ligament short, and not visible externally ; muscular im- 
pressions scarcely visible: hinge strong, with a double 
cardinal tooth in each valve, and two lateral teeth of a 
triangular shape in the right valve, and four teeth in the 
left valve. Animal greyish, sometimes reddish or brownish; 
siphons pale grey, elongated, truncate. Length 6 lines; 
breadth 4 lines; thickness 33 lines. 
Habitat.—Ditches, marshes, ponds, canals, and rivers. 
v. flavescens. (Macgill.); Paler, not so large, and 
more globular. (=C. flavescens. Macgillivary. Moll. Ader- 
deen, p. 246.) as 
v. nucleus (Stud.): Smaller and nearly spherical. 
(=C. nucleus. Studer, Kurz. Verzerchn, p. 98.) 
v. Scaldiana (Norm.): Ovate, paler. (=C. Scaldiana 
Worm, Cycl., p..5, £1, 2.) 
v. Pisidiodes (Gray): Shell subtriangular, slightly 
more produced at its posterior slope, ligament only 
