62 
LAND AND ERESH-WATER MOLLUSKS. 
large, subtriangular, succeeded by two very 
minute ones ; tbe uncini are about sixty in 
number; tbe first one is very large, and of a 
remarkable shape; the rest are very slender, 
hooked, and denticulated. 
Each female deposits her egg-capsules in 
clusters of fifty or sixty, on the surface of the 
shell of her neighbour and not to her own; 
sometimes, but rarely, to stones, or to the shells 
of other mollusks. Each capsule contains from 
forty to sixty eggs, but only one embryo is de¬ 
veloped ; for the other eggs constitute the food 
of the young Neritina until it quits the capsule. 
The capsules, which are usually mistaken for 
the eggs, are globular, and consist of two sepa¬ 
rable portions; the upper and larger falls off 
when the young is about to escape; the lower 
portion remains attached to the surface of the 
foster-parents shell, the raised margins of which 
produce small indentations.— Claperede. 
The young appear in August and September, 
and creep about on the shells or stones which 
bore their egg-capsules, feeding on the micro¬ 
scopic organisms, diatoms, algas, &c., which now 
serve for its nourishment. 
Family Littorinidje. 
The three following species have little claim 
to be regarded as fresh-water shells; the above 
