SO NATURAL HISTORY. [EAST. ZOOL. 
The animals of the remainder of the families live free, moving about 
from place to place, and are mostly marine. 
The family Carditidce have the mantle-lobes free, but united behind 
so as to form one or two svphonal holes. The shells have very oblique 
cardinal teeth, and the cartilage is external: they have no lateral teeth, 
and the periostraca is thin. 0UA > 
The family of Crassinidce only differ from the former in the teeth 
being triangular and diverging like the Verier idee, and they are covered 
with a thick brown periostraca ; the hinder lateral tooth of the left valve 
is double. The Astarti are cordate, compressed, concentrically grooved 
shells. The Cardinice are elongated fossil shells^which have been con¬ 
founded with the Uniones. A orlr-C(P^b 
The family of Crassatcllidce are nearly similar, but they are at once 
known by the cartilage being place dm an internal triangular pit near 
the cardinal teeth. 
The family of Isocardiadje have the very oblique cardinal teeth 
and the linear external cartilage of Cardita , but the hinder lateral teeth 
of the right valve are double. ^id UA> 
The family of LuciNiDiE hafe an orbicular white shell, with none or 
only a few very small cardinal teeth, and the mantle lobes are more or 
less united together beneath, leaving only a hole for the elongate strap- 
shaped foot. They have a single, conical, contractile anal syphon over 
the aperture for the entrance of the water; the front adductor muscle is 
very long and high, and the inner disk of the shell is opake and rugose. 
m general the cartilage is marginal under the ligament, but in Loripes 
it is internal in an elongated pit, and Ungulina scarcely differ from it. 
The Lucina have an external ligament and distinct cardinal teeth; 
the Semeie are like the former, but the valves are unequal, one being 
nearly flat, and it has no lateral teeth ; the Lenticularia are solid 
shells, like the Lucina , but with the cartilages partly internal, they have 
a conical anterior lateral tooth, like Artemis , and Diplodonta are like 
Lucina , but have no lateral teeth. The Cyrenella are subglobose shells 
covered with a thin olive periostraca, and thin teeth. The Corbis are 
thick, ovate, cancellated shells, with distinct cardinal teeth. The Cryp - 
todons are thin shells with a distinct fold on the hinder side, and very 
small teeth. The Verticordice are fossil shells, allied to the latter. 
The family of Unionidce, or of Pond Muscles, are, like the Etherice , 
only found in fresh water; they are covered with a hard olive perios- 
fc<A / v 7 traca, under which the shell is hard ?*nd beautifully pearly. The mantle- 
lobes are free all round, except at the dorsal edge, the hinder edge form- 
r ing, when in conjunction, two holes to the passage of the water, food, or 
rejectamenta, the upper small, simple, the lower one larger, bearded 
on its edge. The cartilage is always marginal, and the hinge presents 
several modifications, but is always destitute of any cardinal teeth; in 
Anodon it has no teeth at all; in Unio , Damaris, &c., it has lateral 
teeth of different degrees of developement and form, so that they some¬ 
times resemble cardinal ones. 
The family of Iridinidce are very like the former, but the hinder parts 
of the mantle are united and produced into two short, unequal, separate 
syphons. The shell is solid, and the hinder part of the submarginai 
scar is more or less indexed. In Iridina and Leila the hinge edge is 
