THE COMMON SHREW 91 



of the unicuspids of the upper jaw is different. In both species they 

 decrease in size gradually from front to back like a flight of stairs, but, 

 whereas in minutus the first three teeth are not of markedly uneven 

 size, in araneus the third is very distinctly smaller than the second, so 

 that the "step" between these two teeth is abrupt. In both species 

 the last unicuspid is minute, especially so relatively in araneus, in which 

 it often lies so much interior to the general line as to be barely visible 

 from the outside. In the first upper incisor the posterior lobe is 

 relatively thicker than in vS". mmutus, the length of its base being about 

 equal to that of the base of the anterior cusp ; and in the first lower 

 incisor the three lobes diminish regularly in basal diameter from front 

 to back, but with the largest gap between the first and second. But it 

 must be remembered that all these distinctions, except the first and last, 

 undergo fundamental alterations as the sharp points of the teeth wear 

 away with age and use. 



Geographical variation : — The colours of the British Common 

 Shrew {S. a. castaneus) are duller than those of 5". a. araneus, which 

 is a brighter and more distinctly tricoloured animal, ranging from 

 eastern Skandinavia to central Europe, and, as stated above, probably 

 also to the east of England. Each of the above has the tail as a rule 

 less than, or not exceeding, 45 mm. long. Two other sub-species, 6". a. 

 tetragonurus (Hermann), of the Alps and neighbouring regions east to 

 Transylvania, and vS. a. pyrenaicus of Miller, of the Pyrenees, are char- 

 acterised by a tail usually exceeding 45 mm. in length. The former 

 is a darkly-coloured animal with the back frequently blackish in 

 summer ; in the latter the back is never blackish in summer. Miller 

 has further described : — S. a. euronotus of the plains of south-western 

 France, a dully coloured animal, with slight cranial peculiarities ; 6". a. 

 /retails of Jersey, with the rostrum deepened and broadened, and the 

 anterior teeth enlarged ; 5. a. gi'anarius, known only from Segovia, 

 Spain, the smallest known form, with a skull resembling that of 5. a. 

 f retails ; and 5. a. bergensls, a large dark shrew from the Atlantic 

 slope of western Norway. vS", a. santonus (Mottaz), from Charente, 

 France, has blackish under-parts not in contrast with the back. 

 Miller unites my 6". a. carpathicus from Transylvania with 5. a. 

 tetragonurus (see Barrett-Hamilton, Ann, and Mag. Nat. Hist., May 



1905, 505-508). 



Another sub-species, 5. a. borealis of Kashtchenko, described from 

 western Siberia, is not available for examination. No doubt the American 

 .S". richardsoni, being only distinguishable from 6". araneus by its longer 

 coat, slightly darker coloration, and some details of dentition, may be 

 regarded as of merely subspecific value. 



