118 CLASS ACEPHALA. 
this family by their ligament being internal and lodged 
throughout in a triangular depression, as in the oysters ; they 
all have a compressed foot fit for crawling. In the 
MactTrRA, Lam., 
Or the Mactre properly so called, the ligament is accompanied 
on the left valve, before and behind, by a projecting plate, 
which is received by two otlers on the right one; close to 
the ligament, near the lunule, is, on each side, a little plate 
chevron-formed. ‘The tubes are united and short. 
After abstracting the lavignons and lutrarie, the genus 
mactra of Gmelin may remain; the species, however, are far 
from being well distinguished. Add Mya Australis, Chemn. 
Some of these mactre are found on the coast of France. 
In the LAVIGNONS the lateral plates are almost effaced ; 
but a single small toothis observable near the internal ligament; 
there is also a second and internal ligament. ‘The posterior 
side of the shell is the shortest; the valves are somewhat 
open, and the tubes are separate and very long, as in the 
telline. 
There is one found on our coast (Mya hispanica, Chemn. 
VI. i. 21), which lives in the ooze, at the depth of several 
inches. 
The fifth family of testaceous acephala, or that of 
INCLUSA, 
Have the mantle open at the anterior extremity, or near the 
middle only, for the passage of the foot, and extended from the 
other end into a double tube, which projects from the shell, 
whose extremities are always gaping. Nearly all of them live 
buried in sand, stones, ooze, or wood. Those of the genus 
Mya, Lin., 
Have but two valves to their oblong shell, the hinge of which 
