140 
which there is a mixture of black Clay : it lies between 
strata of ochraceous Clay and gravel, over a bed of white 
sand about an hundred feet deep, thatrests upon Chalk. 
Some shells contain enough of the animal matter to give 
them consistency, and have a shining surface : I have one 
pair in which the cartilage of the hinge remains, others 
are chalky and moulder between the fingers. The same 
species occurs in sand at Plumstead, of all sizes, even to 
minute. 
I suppose Parkinson considers it the same as the fol- 
lowing species, which he figures as C. deperdita of La^ 
marck, but is too angular to answer Lamarck’s description : 
not having seen the French shell I am still in' doubt. 
CYCLAS cuneiformis. 
TAB. CLXIL— Fig. 2 and 3 . 
Spec. Char. Transversely cuneato-ovate, gibbous, 
lines of growth numerous, fine ; central hinge 
teeth three ; lateral ones two. 
Syn. C. deperdita. Park. Org. rem. 3. 189. 1. 13./. 5. 
The only difference between this and the last is the an- 
gular form of the anterior side, and the greater width. 
I have many specimens of this, both from Charlton 
and Plumstead ; it has also been found at New-cross, 
near Deptford. All the specimens agree precisely with 
Parkinson’s figure, above quoted. 
CYCLAS obovata. 
TAB. CLXIL— Fig. 4, 5, and 6. 
Spec Char. Obovate, gibbous, anterior side ob- 
tuse ; beaks large ; central hinge teeth three ; 
lateral ones two. 
The equality of the length and breadth distinguish this 
shell : the lines of growth are rather strong, but irre- 
gular ; it rarely exceeds three quarters of an inchin length. 
The Clay of Barton Cliff is plentifully supplied with 
this Cyclas : I have received it from thence by favour of 
the Rev. W. Bingley, Iremonger, &c. and I have found 
a variety, exhibited in the larger figure, at New-cross. 
