ARVICOLA 395 



Remarks. — There can be no doubt that Schmidtgen is justified 

 in separating this form from recent Arvicola. It is evidently 

 closely related to the species described above from the earlier 

 Pleistocene deposits of Britain ; but the precise status of these 

 forms cannot be determined with existing materials. 



5. Arvicola amphibius Linnaeus. 

 (Synonymy under subspecies.) 

 Range. — Great Britain. In a fossil state known only from 

 Holocene deposits. 



Characters. — Size large; hind-foot usually 30-34 mm., but 

 occasionally larger, ranging up to 38 mm. ; condylo-basal length 

 in adults ranging between 40 and 44-6 mm. General form robust. 

 Rhinarium small, only the integument covering the ends of the 

 nasal cartilages naked, divided by a groove continuous with the 

 lip-cleft below. Eyes small, placed midway between muzzle 

 and ears. Ears well developed, though almost hidden in the fur, 

 clothed within and without by rather long hair ; provided with a 

 well-developed naked meatal valve or antitragus, which when the 

 ear is closed fits the lower border of a similar but more highly 

 placed valvular ingrowth (" tragus ") from the anterior or inner 

 margin of the ear. Hands large and broad, not specially modified, 

 but hair along the external margin somewhat lengthened and 

 stiffened to form an incipient swimming fringe ; each with five 

 digits, the thumb being very small; the third digit is the 

 longest, slightly exceeding the fourth, which is slightly longer 

 than the second ; the fifth digit is much shorter, only about half 

 the length of the fourth ; all with the exception of the thumb, 

 which bears a small laterally compressed nail, armed with short, 

 sharp, slender and slightly curved claws. Palms naked, with 

 five large pads; the skin between the pads finely wrinkled or 

 granular and forming scaly annulations upon the lower surfaces 

 of the digits. Feet large, with incipient swimming fringes (most 

 noticeable in old individuals), upon both the inner and the 

 outer margins ; with five digits related to each other substantially 

 as in the hands, the first or hallux being, however, less reduced 

 than is the thumb ; all including the hallux armed with claws, 

 like those of the fingers, but longer and stouter. Soles naked, 

 like the palms, but the region between the heel and pads some- 

 I times (particularly in young individuals) pubescent. Plantar 

 tubercles variable, apparently undergoing reduction ; five usually 

 present, the postero-external pad being usually suppressed ; in 

 some specimens the postero-external pad is clearly developed 

 though small ; in others a small supplementary pad is developed 

 to the outer side of that lying at the base of the fifth toe ; in one 

 specimen the pads are not differentiated, but are represented 

 I merely by a tumid mass of flesh. Tail long, from one-half to 

 I two-thirds of the length of the head and body ; clothed with 



