410 MICROTINiE 



For cranial and external measurements, see tables at end of 

 volume. 



8. Arvicola scherman Shaw. 

 (Synonymy under subspecies.) 



Range. — Central Europe from the Baltic southwards to the 

 Pyrenees and from the coast (probably) eastwards through the 

 Swiss Alps to the Tirol (at least). Limits of distribution unknown. 



Characters. — Size considerably smaller than in other species of 

 Arvicola, hind-foot 22-25 mm., condylo-basal length 33-36-6 mm. 

 External and cranial characters more modified for terrestrial 

 and fossorial habits than in other species. Incisors projecting 

 from the mouth more conspicuously, less concealed by the lips 

 than in normal aquatic species. Palmar and plantar tubercles 

 more or less reduced in size. Skull with incisor teeth straightened 

 and protruding ; the rostrum shallow in relation to the cranial 

 depth ; the braincase short and broad, moderately angular 

 and ridged in adults; the occiput obliquely truncated, the 

 supraoccipital sloping forwards and upwards, with the crest for 

 the ligamentum nuchce well defined. Angular processes of mandible 

 often reduced. Cheek-teeth rather small and light, but of 

 normal pattern. 



Geographical differentiation. — Three rather well-marked sub- 

 species are at present recognized, viz., the typical form with a 

 wide range over the lowlands of West-Central Europe, A. s. 

 exitus, inhabiting the Swiss Alps and Vosges Mountains, and 

 A. s. monticola, its representative in the Pyrenees. Of these the 

 typical form {A. s. scherman) is the least specialized, and its habits 

 are partly aquatic, partly terrestrial ; it is not improbable 

 that this subspecies will be found to intergrade to the north, 

 probably in the neighbourhood of the Baltic, with A. terrestris. 

 In the Alpine A. s. exitus and the Pyrenean A. s. tnonticola the 

 specialization is extreme ; although, where circumstances render 

 it possible, these subspecies may lead a partly aquatic life, there 

 is no doubt that in many districts their habits are purely terrestrial 

 and fossorial like those of the niole. These mountain forms are 

 much alike externally, but the auditory bullae are much smaller, 

 flatter and less inflated in A. s. exitus than they are in A. s. 

 monticola, which in this respect is more like ordinary members 

 of the genus. 



The Museum has acquired three or four skulls from Dr. 

 Pfizemnayer which are said to have come from various places in 

 the Caucasus, in the neighbourhood of Tiflis. It is, of course, 

 possible that some such animal occurs in that region ; but the 

 skulls are so like normal skulls of A. s. exitus that I am 

 inclined to think that some error as to locality has been made. 

 In any case it would not be safe to base any conclusions upon such 

 material. 



