2 LAND AND FRESH-WATER MOLLUSKS. 
structure, the animals comprised in each being 
constructed upon a plan differmg from that of 
any of the other divisions. These primary 
groups, which are called sub-kingdoms, are as 
follows :— 
1. Back-boned animals, termed Vertebrata, 
exemplified in beasts, birds, reptiles, and fishes. 
2. Jointed animals, termed Annulosa; as in- 
sects, crabs, worms, &c. 
3. Soft-bodied animals, termed Mollusca; as 
the common garden snail, the oyster, and cuttle- 
fish. 
4, Hollow-intestined animals, termed Cclen- 
terata ; as the sea-anemone, the coral polype. 
5. Jelly animals, termed Protozoa ; as infusory 
animalcules and the sponge. 
The creatures living in our land and fresh- 
water shells, which form the subject of the 
present volume, belong to the group of soft- 
bodied animals, to which the term Mollusca 
is applied. They have, as the name implies, soft 
and fleshy bodies, not divided into segments, 
without bones or jointed limbs, enveloped in a 
muscular coat called the mantle, and the shell 
with which they are commonly protected is 
composed of either one or two, rarely more, 
pieces: the bodies of some are naked. The 
cuttle-fish and slug are examples which will 
