108 CLASS ACEPHALA. 
One of them is known, which excavatcs coral masses to 
form its habitation. (Chama coralliophaga, Gm., &c.) 
VENERICARDIA, Lam., 
Only differ from the carditz in the circumstance that the pos- 
terior plate of their hinge is shorter and more transverse, which 
caused their approximation to venus; their form is almost 
round. Judging from the impression of its muscles on them, 
their animal must resemble that of the carditz and unios. 
(Venus imbricata, Chemn., &c.; and the fossil species, Lam.) 
Both of them approach the cardia in their general form and 
the direction of their ribs. I suspect that this is also the 
place for the | 
CRASSATELLA, Lam. PAPHTIA, 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, extend- 
ing to both sides, is a triangular cavity for an internal liga- 
ment. The valves become very thick by age, and the impres- 
sion made by the margin of the mantle leads to the belief that, 
as in the preceding, there are no protractile tubes. (Venus 
ponderosa, Chemn. VII. lxix. A. D.) 
The third family of the testaceous acephalz, or 
CHAMACEA, 
Have the mantle closed, and perforated only by three holes, 
through one of which passes the foot ; the second furnishes an 
entrance and exit to the water requisite for respiration, and the 
third for the excretion of feces: these two latter are not pro- 
longed into tubes, as in the subsequent family. It only com- 
prises the genus 
CHAMA, Lin., 
Where the hinge is very analogous to that of a unio; that is 
