PLICATULA. La Marck. 
Syn. Harpax. Parkinson 3, 221. 
Gen. Char. An attached unequalvalved bivalve ; 
hinge composed of two diverging striated 
teeth in the flattest valve, and two or four in 
the hollowest valve, and a small pit between 
them for the insertion of a cartilage. One 
muscular impression in each valve. 
A. genus nearly resembling Ostrea, and which may, 
like it, be divided into two sections, comprehending those 
with plain and those with plaited edges. The general 
structure is the same as in Ostrea, and there is often a 
flat striated space within the beaks, that makes the re- 
semblance perfect; the addition of the diverging .striated 
or perpendicularly sulcated teeth is however sufficient to 
warrant a separation. The two teeth in the flat valve are 
received by hollows in the other, the sides of which are 
crenulated to fit them and the inner edges, raised so as 
to form two similar diverging teeth ; in some species the 
outer edges are also raised, from which circumstance 
Parkinson has been led to distinguish his genus Harpax 
as having four teeth in one valve. The teeth and the 
pits which receive them are, as Parkinson justly 
observes, like those of Trigonia. In the recent species 
the teeth have a deep longitudinal canal upon their edges, 
and a small circular pit between them ; in each valve 
vestiges of both these are observable in the fossils. 
PLICATULA spinosa, 
TAB. CCXLV. 
Syn. Harpax. Parkinson v. 3 , p, 221, tab. 12. 
figs. 14 to 18. 
Spec. Char. Ovate, depressed, spinose ; margin 
entire ; spines adpressed ; smallest on the deep 
valve. 
An irregularly shaped shell, but generally obliquely 
ovate with an angle at the beaks ; the deeper valve has 
