993 
PHOLAS. Linn. 
Gen. Cuar. A transverse bivalve, gaping at both 
extremities, with one or more accessory valves 
upon the back ; no shelly tube. 
Orxx or more accessory valves, an elongated tooth 
within each beak, and a more or less muricated surface, 
are characters that belong to a family of shells, the ani- 
mals of which bore holes in stone or wood for protection: 
the Pholas of Linneus is the head of it: his 'Teredo also 
belongs to it: the first is extremely scarce in a fossil 
state, the latter very abundant: they are both confined 
to the newer strata. ‘The recent Pholades may probably 
be divided into several genera, characterized by the form 
of the valves, or number of accessory plates: the shelly 
tube will always distinguish the Teredo. 
PHOLAS cylindricus. 
TAB. CXCVIII. 
Spec. Cuar. ‘Transversely elongated, nearly cylin- 
drical ; posterior sides muricated, pointed, with 
a sinus in the edge; beaks concealed by a re- 
flexion of the edges of the back. 
Tae general form of this is a slightly compressed cy- 
linder: the valves are transversely striated, and have 
many longitudinal elevations ; where these cross on the 
posterior half, are formed many sharp flat spines, but the 
other side is nearly smooth ; accessory valves have not 
been met with, but from the analogy it bears to P. parva, 
it should seem to be furnished only with one. It differs 
