VIVIPARUS. 139 
Sub-order.—-PECTINIBRANCHIATA. 
Lramily.—-NERIT{D&. 
Genus.—NERITINA Lamarck. 
Shell sub-oblong ; oper cee calcareous and solid. 
N. FLUVIATILIS (z7habiting rivers) Linné. Pl. VIII., f. 4. 
Ovate, solid, glossy, chequered brown, white and purple; whov/s 3; 
spire short ; ofercetdum semi-lunar. A. 84 mm. B. 64 mm. 
This prettily marked shell is found in many rivers, 
streams and canals throughout the British Isles, except in 
Wales and Scotland, where Mr. W. D. Roebuck considers 
it has been ‘‘accidentally imported with river ballast from 
England or abroad.” It is the most solid of our fresh- 
water shells and reminds us of its marine cousins the 
Littoriné so common on seaweed. All the varietal forms 
are connected by gradations of colour and markings. 
Var. I. cerina (Colb.). Lemon coloured. 
Var. II. ¢rifascidta (Colb.). With 3 bands of colour. 
Var. III. unduldéta (Colb.). ‘Transversely banded. 
Var. LV. nzigréscens (Colb.). Uniformly dark coloured. 
Family.—PaLUDINID&. 
Genus.—VIvViPARA Montfort. 
Conoid, ventricose ; ofercee/u7 concentrically striate ; ovo-viviparous. 
I. V. CONTECTA (covered by an operculum) Millet. Pl. VIII, f. 5. 
Conical, diaphanous, fairly glossy, dark green, with darker bands 
of same colour; whorls 7, very convex; suture very deep; mouth 
almost.circular, but angulated above ; wszbz/zcus small, but deep and 
distinct ; ofercu/um horny, thin. A. 38mm. B. 31 mm. 
