202 PECTINIBRANCHIATA.— PALUDINADZ. 
by the common Periwinkle, in which each of the 
infant animals is seen enclosed in its proper 
globule, and covered already with a shell of a 
single whorl. 
The Periwinkle (L. littorea) is 
subject to much variation in 
form, colour, and markings; it 
is generally about an inch in 
height, globose, very thick, with 
the margin thin; the colour is 
russet brown, or olive, sometimes 
yellowish, with spiral bands of 
black. The ground colour oc- 
casionally becomes a rich orange 
: or scarlet, with or without black 
PERIWINKLE. bands; and these varieties are 
very handsome. 
FAMILY PALUDINADA. 
(Marsh Snails.) 
This is a group of fresh-water Mollusks, so 
closely resembling the Periwinkles in many of 
their characters as to have been confounded with 
them by Cuvier and other zoologists. ‘Those cha- 
racters are as follows :— 
The shell is conical, spiral, thin in texture, 
covered with an olive-coloured skin; the orifice is 
ovate, entire, but angular behind. The animal 
has a muzzle-shaped head, and long, slender ten- 
tacles, with eyes seated at the outer side of their 
bases ; the gills are always enclosed in the breathing 
cavity. An operculum 1s always present, generally 
horny, but sometimes shelly, formed of concentric 
