374 
THE OCEAN WORLD. 
and by no means of an agreeable flavour, is a great resource to tbe 
poor Indians. The accompanying representations of Tridaena sqi* ar 
mosa (Figs. 158 and 159) will convey a general idea of tbe genus.. 
In tbe small family of which 
we have made the Tridaena 
tbe representative, as well as 
in some preceding families, 
the mantle of the animal is 
more or less largely open, 
but never with such a p r0 ' 
longation as to form tubes. I u 
the Cardiums, now under con* 
Fig. 159. Tridaena squamOBa, on the inside (I.amarck). gjderation US Well as DoMtt®’ 
Tellina, and Venus, the respiratory organs are somewhat modified, s J 
as to adapt them to the habits of the animal. All these molluscs 
live buried in the mud or sand, and two great tubes issuing from f 
interior of their bodies bring the atmospheric air into communicate 11 
with their respiratory organ — namely, the branchial leaves. 
Tho Cardiums, so called from the fancied resemblance which m°s 
of the shells bear in shape to a heart (icaphla), are abundantly diffus^ 
in every sea. The shell is convex, as we see in G. Mans (Fig. lb /’ 
Fig. 160. Cardium liians (Brocchl). 
Fig. 161. Cardium Greenlandicum 
(Che ® 0 * 1 
ita0» 
some what heart-shaped, equivalved, the edges dentate or corrugn*^ 
the hinge furnished with four teeth upon each valve. The acces^ 
ornaments vary with the species, some being smooth, as in - ,Ll> 
