57 
ASTARTE excayata, 
TAB. CGXXXIIX, 
Spec, Char. Obovate, convex, concentrically 
costated ; anterior side truncated ; lunette he- 
mispherical, excavated ; cartilage enclosed 
in a sulcus ; margin toothed. 
N early one-third wider than long, with the back arched ; 
the beaks obscure, much inclined towards the posterior 
side, which is small. The lunette varies much in form, 
being narrow in young and broad in old shells, it is so 
deep that the cast of it resembles a globose bivalve. The 
furrow on the back for the reception of the cartilage is also 
deep, butit is very narrow and boundedby sharp edges that 
nearly approach each other. The costae are not very much 
risen in any part, and near the front of large shells dege- 
nerate into irregular undulations. There are strke upon 
the hinge teeth that might lead a casual observer to take 
it for aTrigonia. 
Mr, Miller’s collection contains the only exposed 
hinge I have seen, and the most perfect specimen for 
explaining the excavated lunette ; it is from Dundry. 1 
have specimens also from G W, Braikenridge, Esq» 
from the same place. 
