37 
TEREBRATULA plicatilis. 
TAB. CXVIII.---Fig. 1. 
Spec. Cuar. Gibbose, transversely obovate, finely 
and obtusely plaited ; middle elevated by twelve 
plaits; fifteen or more plaits on each side ; 
beak slightly projecting. 
Lee rather greater than the depth; width about one 
third greater than the length. The plaits continue to 
near the beak. The beaked valve is rather less gibbose 
than the other. 
L have this species most perfect from the upper Chalk 
at Northfleet near Gravesend, and also filled with flint 
from Margate: it is sometimes in such a state as to sepa- 
rate from the chalk, and show something of the interior 
construction, which is very desirable in this division of 
shells, as it is often very remarkable. The two upper 
figures are the upper and lower valve separated from the 
chalk, and showing the construction of the hinge. The 
next figure shows both valves closed together. 
TEREBRATULA octo-plicata. 
TAB. CXVIIL.---Fig. 2. 
Spec. Cuar. Gibbose, transversely obovate, ob- 
tusely plaited ; middle elevated by eight plaits ; 
twelve or fourteen plaits on each side; beak 
projecting. 
Tans differs from the last in the number of plaits, having 
at most but 9 at the sinus, itis also a rather longer shell, 
