58 - - ZOOLOGY. 
Fam. 1. Mactride. Hinge with an erect V-shaped tooth, ligament 
internal. The genus Jactra, Linn. (pl. 76, fig. 40), includes sub-trigonal 
shells which are slightly gaping; hinge with a concave tooth to receive the 
ligament; two additional striated teeth near the hinge. This genus 
contains shells which sometimes attain a considerable size. I. solidissima, 
Chemnitz (Gould, Jnvertebrata of Massachusetts, p. 51), of the United 
States coast, is sometimes found six inches long and four in height. In this 
family the foot passes through an opening in the mantle, and the two 
siphons, although distinct, are inclosed in a common integument. Some 
authors place this family among the Elatobranchia. Lutraria lineata, Say, 
American Conchology (pl. 9). LZ. plicatella, Lamarck, vol. vi. p. 98. 
Fam. 2. Myide. This family is differently divided i different authors, 
some including the two groups of which Osteodesma and Solemya are the 
types, whilst others believe that these should form distinct families. In 
Mya the shell is gaping, and there is a broad spoon-shaped tooth projecting 
from the hinge to the opposite valve, where there is a cavity to receive it. 
The labial palpi are long, stout, and pointed. The mantle is closed, except 
a small anterior opening for the passage of a slender foot, and the ordinary 
openings for the siphons, which are very long, and inclosed in a common 
envelope. This genus buries itself in the sand, with the exception of the 
end of the siphons. Jfya arenaria, which has a shell three or four inches 
long, inhabits both sides of the Atlantic, between high and low water-mark. 
It is extensively used in New England as food, under the name of clam, 
a name which is applied to Venus mercenaria in the middle States. The 
genus Corbula forms part of the restricted family of Myade. 
In the opinion of some authors, Osteodesma and the allied genera Lyonsia, 
Periploma, Thracia, and Anatina, form a family, although the aggregate of 
these genera seems to have no higher rank than that of a sub-family. 
Some of the shells are of an extremely delicate texture; these have no 
cardinal teeth, and there is an ossiculum or accessory bone forming part 
of the mechanism of the hinge, upon which Deshayes has founded the 
family name Osteodesmacea. Mya norvegica was at first the type both of 
Lyonsia, Turton, 1822, and Osteodesma, Deshayes, 1835, but the latter 
author subsequently admitted Lyonsia, and applied his own term to a 
different group. Couthouy’s paper in the third volume of the Boston 
Journal of Natural History, and Gould’s Invertebrata of Massachusetts, may 
be consulted upon these genera. 
Fam. 3. Solemyide. The genus Solemya is by some considered as 
forming a distinct family, whilst by others it is placed in the family of the 
Solenide. Some of its characters are very distinct; the branchiz are thick, 
and single upon each side, and they are divided so as to resemble those of 
Crustacea. The foot is truncated and shaped like a sucking disk; the 
posterior half of the mantle is closed, the siphons are short, aa the 
-periostraca of the shell projects in a flap, far beyond the pales 
portion. 
Fam. 4. Sawicavide. This family includes Saxicava and Byssomia. 
The first contains small species and secretes a byssus. The cardinal teeth 
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