670 



RODENTIA 



Diagnosis. — Size and cranial characters as in the large 

 Microtus agrestis agrestis of Norway and Sweden ; first upper molar 

 with small third inner loop usually present (in ten among fourteen 

 skulls examined), almost as well developed as postero-internal 

 loop in second tooth ; colour of underparts more brownish than 

 in the other races. 



Colour. — Upper parts and sides darker and clearer (less 

 russet) brown than in M. agrestis hirtus and M. a. neglectus, 

 essentially as in true agrestis ; underparts rather heavily washed 

 with brownish buff, this suffusion in many specimens becoming a 

 definite, rather light ochraceous-buff. 



Skull and teeth. — The skull is not distinguishable with 

 certainty from that of true Microtus agrestis, 

 but is at once recognizable among those of 

 the British races by its large size. Teeth 

 with no peculiarities other than the unusual 

 frequency with which a definite postero- 

 internal loop is present in m^. This occurs 

 in no less than ten of fourteen skulls ex- 

 amined, while in specimens of the other 

 races it is present only eight times among 

 136 skulls. 



Measurements. — External measurements of 



type (adult female) : head and body, 123 ; 



tail, 44 ; hind foot, 19 ; ear from meatus, 12. 



A second female from the same locality : 



head and body, 111 ; tail, 39 ; hind foot, 



18" 5; ear from meatus, 12. Adult female from Loch Boisdale, 



South Uist : head and body, 111; tail, 44 ; hind foot, 18-5; ear 



from meatus, 12. For cranial measurements see Table, p. 677. 



Specimens examined. — Fourteen, from the following localities in the 

 Hebrides : North Uist, 11 (B.M. and Edinburgh) ; Loch Boisdale, South 

 Uist, 3 (Edinburgh). 



BemarJcs. — This form is of unusual interest on account of the 

 presence as a normal character of a peculiarity of the enamel 

 pattern occurring elsewhere in the species as a rather rare 

 anomaly.* Its general unlikeness to the other British forms and 

 similarity in certain respects to true agrestis of Scandinavia is 

 also worthy of special note.f 



S, 3 9. N. Uist, Hebrides. J. F. Davison (c & p). 6. 3. 1. 1-4. 



(6. 3. 1. 3. Ty2ye of subspecies.) 

 1 al. N. Uist. J. A. Harvie Brown (p). 79. 9. 18. 2. 



* A postero-internal loop in m* is sometimes found in the American 

 Microtus pennsylvanicus, a species with the same enamel pattern as 

 M. agrestis. Such a tooth is figured in North American Fauna, No. 12, 

 fig. 1. July 23, 1896. 



t For a discussion of the general problems of distribution involved in 

 this animal's presence in the Hebrides, see Stejneger, Smithsonian Miscell. 

 Coll., XLViii, pp. 458-512, May 4, 1907, and Naturen (Bergen), xxxii, 

 pp. 193-202, 269-277, July-September, 1908. 



Microtus agrestis exsitl. 

 Enamel pattern. X 5. 



