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. 



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. 



XXXIV. — On the Occurrence of two Species of Shells of the 

 Genus Conus in the Lias, or Inferior Oolite, near Caen in 

 Normandy. By C. Lyell, Esq., F.R.S., F.G.S., &c. 



The 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 



