NOTES ON TWO COLLECTIONS OF MICE 225 



(12) length of diastema; (13) length of incisive foramina; 

 (14) width of incisive foramina; (15) width of rostrum; 

 (16) least width (at base) of the anterior root of the zygoma 

 (" masseteric plate ") ; (17) length of cheek-teeth (on crowns). 

 In the lower half of Part I. these dimensions are reduced to 

 percentages of the condylo-basal length ; the reductions were 

 made with a slide-rule. 



In Part II. of the table the skulls from Barvas are 

 compared with those from Stornoway and with those from 

 the neighbourhood of Uig, western Lewis — the latter being 

 typical A. ii. hebridensis. At the top the range of the 

 condylo-basal length found in skulls with well- or much- 

 worn teeth is given, and the average length for each series 

 is printed in heavy numerals. The remainder of this part of 

 the table compares similarly the percentages of the condylo- 

 basal length formed by each of the 17 dimensions — the 

 range of the values in each series of skulls being printed in 

 ordinary, the average values being in heavy numerals. 



It will be seen from Part II. of the table that, as regards 

 absolute size, the Barvas skulls, like those from western 

 Lewis, are larger than those from Stornoway. As regards 

 proportions, however, the Barvas skulls agree very closely 

 indeed, in most respects, with the Stornoway series, and 

 offer similar rather well-marked distinctions from the skulls 

 of typical A. h. hebridensis. The possibility of the existence 

 of two races of hebridensis upon Lewis has been discussed 

 not only in the works above cited but in the earlier papers of 

 de Winton and Barrett-Hamilton. The Barvas collection is 

 of interest in proving that the range of the Stornoway or 

 eastern race extends across the island to the north-western 

 coast, where, although the skull attains the slightly larger 

 size of typical hebridensis, the cranial proportions remain 

 essentially as in specimens from north-eastern Lewis. Before 

 we can come to any decision as to the true status of the 

 Field Mice of Stornoway and Barvas, we need a good series 

 of specimens from the hilly country to the south of the small 

 east and west stream, which cuts off Barvas from the Uig 

 district or type locality oi A. h. hebridensis. 



