ORDER TESTACEA. 115 
penetrating between the plates of the other valve; in the 
middle are two teeth frequently but slightly apparent. The 
shell is orbicular, and without any impression of the retractor 
muscle of the tube ; that of the anterior constrictor, however, 
is very long. Possessing similar traits of character with the 
loripedes, their animals must be analogous. (Venus Pennsyl- 
vanica, Chemn. VII. xxxvii. 394—396, &c.) 
The living species are much less numerous than those that 
are fossil; the latter are very common in the environs of 
Paris. (Lucina saxorum, Lam., &c.) 
We should approximate to the lucine the UNGULIN&, 
which also have an orbicular shell and two cardinal teeth ; 
the lateral ones, however, are wanting, and the anterior mus- 
cular impression is not so long. (Ungulina transversa, Kam., 
Sowerb., Gen. of Shells, No. X.) The genus 
VENUS, Lin., 
Comprizes many testacea whose general character consists in 
the teeth and plates of the hinge being approximated under 
the summit in a single group ; they are usually more flattened 
and elongated in a direction parallel to the hinge than the 
cardices. The ribs, when there are any, are almost always 
parallel to the edges, being directly the reverse of their arrange- 
ment in the cardia. 
The ligament frequently leaves an elliptical impression 
behind the summits, which has received the appellation of 
vulva; and before these same summits there is almost always 
an oval impression termed the anws or lunula. 
The animal is always furnished with two more or less pro- 
tractile tubes, sometimes united, and with a compressed foot, 
which enables it to crawl. 
M. Lamarck appropriates the name of VENUS to those 
which have three small diverging teeth under the summit. 
12 
