82 Lamarck’s Genera of Shells. 
Type. Teredo navalis*. (Idem. Linn.) 
Anteriorly furnished with two short, simple, palmule, ter- 
minated by an operculi-form callus, Pl. iv. Fig. 23. Europe, 
In timber, immersed in salt-water. 2 Species. 
2d Family. 
PHoLaDARtA, (contains 2 Genera.) 
No tubular sheath; shell furnished with accessary pieces 
not belonging to the valves, gaping anteriorly. 
Formerly the pholades, balani, and chitones were considered 
as multivalve shells, and forming a separate division ; it is now 
known however that allthe pholades are equivalve and regular 
bivalves ;that their valves are united bya hinge, and that conse- 
quently they all belong to the class Conchifera. But in addition to 
the two constant valves, these shells have other singular pieces, 
always smaller than the true valves, that must be considered 
as accessary, for their number varies according to the species, 
The ligament is external, but covered and concealed by the 
accessary pieces. The pholadaria are borers and bury them- 
selves in stone, wood, and madreporic masses, or the sands, 
living solitarily. 
1. Pholas+. 
Animal inhabits a bivalve shell, which almost wholly covers 
its body ; protrudes anteriorly two united tubes, often surrounded 
by acommon skin, and, posteriorly, a foot, or short muscle, 
very thick, flattened at its extremity. No tubular sheath. 
Shell generally thin, fragile, bivalve, equivalve, gaping at 
both sides, having different accessary pieces, either on the 
hinge, or below it. Lower or posterior edge of the valves 
curved outwards. 
Type. Pholus dactylust. (Idem. Linn.) 
Shell elongated, posteriorly narrow-beaked, posterior ribs 
denticulated ; anterior side not ribbed, extended. 
European Seas. Pl. iv. Fig. 24. 9 Species. 
* Of the ships. + From ¢wAeos, latibulum, a burrow. 
$ Date? 
