376 
MOLLUSCA. 
the sand or mud by means of a large, com- M 
pressed, and nearly quadrangular foot. The m 
posterior end of the cloak is garnished with M 
many small tentacula. The Anodontes live in m 
fresh waters. m 
We have some native species ; and of the largest ^ 
{Mytilus cpgnetcs, lAnn.) the valves are used to skim 
milk. From its insipidity, the animal is not edible. |j 
M. de Lamarck distinguishes, under the name of q 
Iridina, an oblong species, whose hinge is granu- 
lated its entire length. The cloak of the animal is 
closed a little behind.* The Bipsas of Leach is <:i 
founded on another species, which has the angles i 
more decidedly marked, and a vestige of a tooth in 
the hinge. ' | 
!U 
The Uniones (JJnio, Brug.) — | 
Resemble the Anodontes in the shell and in the - 
animal, but the hinge is more complicated. There 
is a short cavity in the anterior part of the right valve, which receives a short plate or tooth from the 
left one, and behind it is a long plate, which is inserted between two others on the opposite side. 
They also inhabit fresh water, preferring running streams. Sometimes the anterior tooth is more or | 
less large and unequal, as in the My a margaritifera, Linn., whose pearls have been used in making j 
ornaments. At other times this tooth is laminated, as in Mya pictorum, Linn., known to every body ! 
[from its shells being used in holding water colours] . " | 
(A great number of species, remarkable for their size and figure, are found in the lakes and rivers of North | 
America. MM. Say and Barnes [and Lea] have described them, and have proposed some subgenera amongst them.) 
M. Delamarck distinguishes the Hyria, with the angular productions of the hinge so decided that their shell is 
almost triangular. And the Castalia, the shell of which, somewhat heart-shaped, is striated with rays ; and the 
teeth and plates of the hinge are grooved across their longest diameter, which gives them a relationship with the 
Trigonice. 
There ought to be placed near the Uniones some marine shells, which have a similar animal, and very nearly the 
same sort of hinge, but the summits of the valves are more swollen, and prominent ribs radiate from them to the 
margins. These are the Cardita, Brug. Their 
shape is more or less oblong or cordate. In 
some the shell gapes on the lower side. The 
Cypricardia, Lam., are Carditse with the tooth 
under the summit divided into two or three. 
Their form is oblong, and their sides unequal. 
M. de Blainville has again separated the Coral- 
Uophaga, whose shell is thin, and the lateral 
lamina [of the hinge] so much obliterated that it 
might induce us to approximate them to the 
Fig.i9i.-Carditacaiicuiata. Venus. One species is known, that burrows in 
masses of coral. 
ill 
^iS 
Venericardia, Lam., diifer from the Cardita only because the postei’ior lamina of their hinge is more trans- 
verse and shorter, thus making an advance to the Venus : their form is almost round. It may be inferred from 
the muscular impressions that their animal has also a resemblance to that of the Cardita and of the Unio. Both 
of them approach the Cardia in general form and in the direction of their ribs. 
I suspect that this is also the place for the Crassatella, Lam. {PapMa, Roiss.), which has sometimes been 
approximated to Mactra, and at others to Venus. The hinge has two slightly-marked lateral teeth, and two very 
strong middle ones, behind which, extending to both sides, is a triangular cavity for an internal ligament. The 
valves become very thick with age, and the impression made by the margins of the cloak, leads to the belief that 
there are no extensile tubes. 
THE THIRD FAMILY OF THE ACEPHALA TESTACEA,— < 
The Camacea, — 
Has the cloak closed, but perforated with three holes, through one of which the foot passes ; the ; 
second furnishes an entrance and exit to the water required for respiration ; and the third is the vent : , 
the two latter are not prolonged into tubes, as in the following family. j 
* Notwithstanding- the similarity of the shell, Iridina does not belong to this family, but to the Cardiacea. Ed. | 
