THE FIELD MOUSE OF FOULA 



179 



from mere inspection ; in addition they show that the skull 

 of A.f. tJiiileo has some small peculiarities of its own. The 

 absolute size of the skull is about as in f. grantii ; the 

 occipitonasal length, interorbital width, nasal length and 

 width, and the length of the anterior palatal foramina, are 

 dimensions which tend to be smaller relatively than in either 

 of the other two forms of fridariejisis ; on the other hand, 

 the zygomatic breadth, cranial width, and post-molar length 

 tend to increase in relative value. The rostrum is relatively 

 wider than m/./ridariensis, narrower than \\-\ f. gra?itii ; the 

 masseteric plate is relatively narrower than in f. grantii, 

 much narrower than in \.r\xQ fridariensis ; the length of the 

 tooth-row is nearly as in f. fridariejisis, distinctly shorter 

 relatively than \nf. grantii. 



The following tables of measurements furnish material 

 for exact comparison with other British members of the 

 sylvatiais group : 



I. EXTERNAL MEASUREMENTS. 



