292 Mr, Lyell on Shells of the Genus 
the bones composing the zygomatic arch are broader in the young 
than in the adult: how to account for this I do not otherwise know, 
than that it is a contrivance of nature to give greater strength to 
the jaw in the young, before the remainder of the cranium is suffi- 
ciently ossified to bear the strain of the large temporal muscles 
without such support; but on referring to the skeletons of the 
young and old otter, I find the same difference to exist as regards 
the posterior portion of the arch. This, therefore, does not appear 
to be a character of any value. a 
The dentition in all the specimens is the same, and agrees with 
that assigned to the genus; the canines in the adult are, however, 
slightly larger than in the younger one. No other points, through- 
out the whole skeleton, of sufficient importance to call for observa- 
tion, present themselves. I think, however, that my readers, from 
what I have said, will agree with me in saying, that it is at least 
most probable that the young of the Common Marten has been mis- 
taken for a distinct species, and that no such animal as the Pine 
Marten exists in the British Isles. 
It may, perhaps, while on the subject of British animals, not be 
out of place here to advert to a short account of the Irish Hare, 
published by me in vol. ii. p, 283, of the Magazine of Zoology and 
Botany, (1837) since which period another paper on the same 
subject has been published in one of the Irish Transactions, by Mr. 
Thompson of Belfast, to whom I take this opportunity of returning 
my thanks for it. He adverts in it to some disparity between his 
measurements and mine. 
On the receipt of his paper I immediately referred again to my 
skeletons, and found the measurements to agree perfectly with those 
I had already published; but having obtained another Irish Hare 
and another English one, I found that I could compare them 
either so as nearly to agree with his measurements or my own: 
thus a comparison between the second specimens obtained, agreed 
very nearly with Mr. Thompson’s, and the original specimens with 
my own; but a comparison between one of the last with one of the 
first differed from either. 
This, I think, proves the necessity of being very careful in the 
admission of measurements as distinctive marks of species, unless 
the limit of variation in each species is to a certain extent ascer- 
tained. 
XX XIV.—On the Occurrence of two Species of Shells of the 
Genus Conus in the Lias, or Inferior Oolite, near Caen in 
Normandy. By C. Lyeuu, Esq., F.R.S., F.G.S., &c. 
Tur discovery by MM. Deslongchamps and Tesson of fossil 
shells of the genus Conus, in the lias of Normandy, in 1837, 
has by no means attracted the attention it deserves, either in 
