13 
AST ARTE rugatus, 
TAB. CCCXVI. 
Spec. Char. Obovate, anteriorly subtruncated, 
when young transversely costated, after- 
wards slightly wrinkled ; edge internally 
crenelated ; lunette concave, obovate, 
pointed. 
A rather gibbose shell, with a regularly concave 
short lunette ; the costae extend only a little beyond the 
beaks, and are often entirely lost by erosion, although 
the animal probably inhabited ancient seas, if we may 
judge from its analogy to A. Scotica, Danmoniensis, 
&c. to the latter it bears so strong a resemblance that 
it might easily be taken for it, were it not more gibbose 
and smoother, or rather, not regularly costated. Fig. 1 
represents a young individual, the edge of which is not 
crenated, neither are there any crenulations upon the 
edges of those given at figures 2 and 3, but as they are 
chipped all round, it is possible that they may have 
been crenulated when perfect : the entire edge is the 
only character that distinguishes A. Scotica from Dan- 
moniensis : I have doubts respecting its sufficiency, and 
in the present case am not inclined to admit the young 
shell with an entire edge to the rank of a species, since 
it exactly agrees with the marks upon the umbones of 
the larger shells. 
Found at Highgate when the Archway was digging 
through the hill. 
