134 
A single valve only of this muscle has come into my 
hands, for which I am indebted to Mrs. Cobbold, who 
found it at their delightful retreat, Holywells, near 
Ipswich. It seems to be a rare species. 
The resemblance of both these to recent species is 
remarkable ; and we think the latter want more discri- 
mination than has hitherto been bestowed upon them 
even by the most judicious : it is also highly interesting 
to enquire into the peculiarities of other shells of the 
Crag formation which so often accurately correspond 
with the recent species. 
