104 DR. C. I. FORSYTH MAJOR ON PLIOCENE VOLES. [Feb. 18, 



speak, of the fossil tooth. I had before met with a similar 

 feature in one of two very young teeth of the recent amphibius- 

 group, from Pisa, which presumably belonged to Savi's Arvicola 

 destructo7\ In the recent tooth the enamel islet showed a slightly 

 different position and genesis, was quite superficial and therefore 

 ephemeral ; it was associated with some other complications- 

 two additional shallow enamel-loops — which likewise approach 

 the tooth of the very young amphibius to that of the Pliocene 

 form. In the recent species this pattern is very soon worn away ; 

 there is no more trace of it in slightly older specimens. This is a 

 fresh instance of a recent form preserving in the younger stages 

 of its molar the features of a Tertiary form. 



When during the revision of the fossil Rodentia of the British 

 Museum, the Microtidse of the Forest Bed came to be studied, I 

 was anxious to ascertain whether the enamel islet occuiTed there 

 too in adult specimens, as is the case in the Val d'Arno fossil. 



Mr. E. T. N'e\vton has published an elaborate description of 

 the Rodents of the Forest Bed and N^oi'wich Crag, and has shown 

 that the larger Yoles are, by the presence of well- developed fangs to 

 theii' molars, very distinct from the amphibins-type with which they 

 had been confused by all previous writers. He who enjoys the 

 advantage of standing on his predecessor's solid shoulders, has also 

 the duty to try and see a little farther, especially when additional 

 material has accumulated in the meantime. If, therefore, to-day 

 a step forward is possible in the loiow ledge of the Pliocene Voles, 

 it is but fair to acknowledge that this is in a great measure due 

 to Mr. Newton's previoiis work. 



Among the Yoles' teeth of the Savin Collection from the 

 Forest Bed, I found the character alluded to, but only in a 

 relatively small number of teeth {e.g. text-fig. 13, no. 1) and in 

 different proportions according to the localities. "Whilst among 

 55 first molars from the West Runton Upper Freshwater Beds 

 only four showed the character in question, the number of teeth 

 provided with enamel islets was larger among the less numerous 

 Voles' remains from the East Runton Forest Bed, and, more- 

 over, other features became apparent. 



From the Noi-wich Castle Museum I have received of late, 

 through the kindness of Mr. Leney, a small number of teeth and 

 two jaws, here exhibited, which were collected by Mr. Fitch in 

 the Norwich Crag at Thorpe (text-figs. 13, nos. 2-5; 14, no. 15; 

 15, nos. 20, 29). Here the presence of the enamel islet is the 

 rule : there are ten anterior lower molars in this small series — 

 eight exhibit the islet, one is very old and apparently has lost 

 every trace of it; the tenth, a very young tooth (text-fig. 15, 

 no. 29), reveals the genesis of the islet, which is the central 

 portion of the antero-external enamel fold. Moreover, the teeth 

 are of two different sizes. 



In short, the result of the investigation is, that the Voles of 

 the Norwich Crag are different from those of West Runton and 

 are represented by two species ; whereas at East Runton the 



