ARVICOLA 391 



species in which the third outer fold is reduced by insulation while 

 the " prism-fold " persists, no trace has been found at Bacton. 

 Not improbably M. savini died out without issue before the Bacton 

 beds were deposited. 



The mammalia recorded from the Cromerian Beds at Bacton 

 are " Ursus spelceus," Canis sp., Rhinoceros etruscus, Cervus 

 Jitchii, C. sedgwickii, Trogontherium cuvieri, Sciurus, Talpa, Sorex 

 savini, S. runtonensis, " Myogale," and Baloenoptera, in addition 

 to the voles. This is clearly a Cromerian assemblage, but whether 

 all came from one horizon or not is uncertain. In any case, it 

 does not matter very much so far as we are concerned, because 

 some of the remains here referred to A. hactonensis and A. greenii 

 came from the " gravel-pan " which usually forms the base of 

 these freshwater deposits of the Norfolk coast. I suspect that, 

 hke the " Bone-Bed " at the base of the Crags, the " gravel-pan " 

 is of different ages in different localities ; but be that as it may, I 

 think, from the character of the voles that there can be no 

 question that the Bacton (or rather Ostend) deposit is later than 

 is the Upper Freshwater Bed at West Runton. 



Bosco ^ has described, under the name " Arvicola pliocenicus " 

 Major, some teeth of a vole, from the Upper Pliocene of the Val 

 d'Arno, characterized as follows : — " Animale di dimensioni 

 intermedie fra quelle dell' Arvicola amphihius e dell' A. nivalis; 

 con denti molari senza radici e prismi spigoli salienti arrotondati 

 ed il primo molare inferiore con cinque prismi dal lato interno e 

 quattro dal lato esterno." It is evident from what he says of 

 Tuccimei's account of the fossils from Bocchignano, etc., that 

 Bosco is fully acquainted with the characters of rooted teeth, 

 and therefore there is no reason to doubt his accuracy when he 

 describes these Val d'Arno teeth as rootless. If we suppose these 

 rootless molars to be young teeth of Mimomys, then their crown 

 patterns should show some of the ephemeral complications char- 

 acteristic of the young m^ in all known species of Mimomys. The 

 crown views given by Bosco, although not very well drawn, appear 

 to me to be good enough to show that the teeth are in an adult 

 stage of wear and that all ephemeral complications have dis- 

 appeared. It is to be hoped that these specimens will be again 

 examined and carefully figured ; for it seems likely that they will 

 supply an Italian parallel to the Bacton forms. 



3. t Arvicola prsceptor sp. n. 



1890. Arvicola ampkibius Newton, Geol. Mag., [3], 7, p. 453; and in 

 Whitaker, Geology of London, 1, 1889, p. 336 (in part). 



1890. Microtus amphibiHs Woodward and Sherborn, Cat. Brit. Foss. 

 V'ert., p. 365 (in part). 



1901. Microtus amphihius Hinton and Kennard, Essex Nat., 11, 

 p. 348. 



1910. Arvicola sp., Hinton, Proe. Geol. Assoc, 21, p. 492. 



' Bosco, I Roditori Pliocenici del Val d'Arno superiore. Palceonto- 

 graphia Italim, 5, p. 93, Tav. xii (ii), fig. 15, 1899. 



