126 The Official Guide to the 
ing of the shells known as Cockles, with some of 
which we are very familiar. They are a well-defined 
family, inhabiting soft and sandy ground, widely 
distributed in almost all the seas of the world, occur- 
ring from low-water mark to considerable depths. 
Only members of the typical genus Cardium are 
found in British waters; but there are several other 
genera, both tropical and arctic. Some of the 
species have very handsome strongly-marked shells ; 
but perhaps the most interesting to us is Cardium 
edule, the highly-gregarious species, found so abun- 
dantly on our own coast, and which furnishes not 
only an agreeable esculent, but also helps materially 
in the liveiihood of very many persons, not only on 
our own, but on all the sandy shores of the kingdom. 
The family Cyprinrp# contains four genera and six 
species. They are all inhabitants of sandy and 
muddy tracts of the sea bed, and with the exception 
of the first, /socardia, the “ Heart Cockle,” so called 
from the globular and cordate form of its very 
handsome shell, all bear a strong family likeness. 
Cyprina tslandica is a handsome species, oval in out- 
line; in Astarte the shell is more compressed, and 
Circe has a thick compressed orbicular shell, with 
diverging striz. The shells of the next family 
VENERID&, which is a numerous one, much resemble 
those of the preceding in form, and are noted for the 
beauty of their colours and markings. V. “incta 
and chione may be pointed out. Many species of the 
family Tetuinip@ follow, some of them extremely 
pretty and delicate shells. Of the family Macrripa, 
Mactra solida and glauca are fine species, as also 
Lutraria elliptica, and the various species of Scro- 
bicularia. 
The next family brings us to a very different form 
of shell, although the animals still have the same 
