158 SPHERIIDA. 
taken for P. fontinale, as the latter shell is not so deeply 
grooved and is far more ventricose. 
Var. I. -devitiscula (Mogq.). Larger, strice faint. 
Var. II. flavéscens (Mog.). Uniform pale yellow. 
2. P. FONTINALE (2nxhabiting springs) Draparnaud. 
Pipi xX, .1.6, and Pl. X.; f. 1. 
Triangular, tumid, thin, greyish horn-colour; more transparent 
than P. amnicum; beaks prominent; scars deep. L. 3% mm, 
B. 4—5 mm. 
Found in sluggish streams, canals, ponds, and ditches 
throughout the British Isles. ezs/owana is a common 
and very distinct form. 
Var. I. Aénslowdna (Shepp.). ‘The valves have a ridge 
near the beaks. 
Var. II. pulchélla (Jen.). Glossy, strongly grooved. 
Var. III.. cinérvea (Ald.). Larger and flatter. 
Var. IV. pdliida (Gas.). More ventricose ; irregularly 
striate ; paler with a few darker rays which diverge from 
beaks to margin. 
3 P. PuUSsILLUM (swlall) Gmelin. Pl. IX.,'f.7, and Pie 
Oval, thin, moderately glossy, finely striate concentrically, yellowish 
white; deaks nearly central ; /¢gament inconspicuous. L. 42 mm. 
B. 5 mm. 
This is far the commonest species. It is found in 
ditches and swamps, ponds, etc., throughout the British 
Isles. Its oval form as well as its more central and 
