6 ANNALS OF SCOTTISH NATURAL HISTORY 



The face of M. orcadensis resembles that of M. agrestis 

 in regard to its width. It is narrower than in E. glareolus, 

 and broader than in M. ampJiibius. 



If the length of the cranium is compared with the length 

 of the face, it is found to be slightly less in M. orcadensis 

 than in M. ampJiibius, and decidedly less than in M. agrestis 

 and E. glareolus. 



When the length of the face is compared with the length 

 of the entire skull, M. orcadensis has a slight advantage over 

 M. amphibius, and a decided advantage over M. agrestis and 

 E. glareolus. Taking the two foregoing statements together, 

 it is evident that the face is longer in M. orcadensis than in 

 any of the others. 



The relative width of the palate is slightly greater in 

 M. orcadensis than in M. ampJiibius t but distinctly less than 

 in M. agrestis and E. glareolus. 



The molar teeth of M. orcadensis possess certain features 

 to which attention must be directed. The number of 

 enamel-spaces in the first upper molar is 5 ; and in the 

 second, 4. In the third molar there are clearly 5 spaces, 

 but the most posterior is partly divided into two. When 

 this tooth is compared with the corresponding tooth of 

 M. agrestis there is found to be a striking similarity. In 

 M. agrestis there are 6 spaces. Therefore it may be 

 claimed that in M. orcadensis there are also really 6 spaces, 

 but the posterior two are not completely separated from each 

 other. It is conceivable that, if other specimens were 

 examined, separation might be discovered even greater than 

 that shown in Fig. i, A 3. 



The spaces in the lower molar teeth are shown in outline 

 in Fig. 2, A. The first molar has 9 spaces ; the three most 

 anterior being incompletely separated, as is the case in 

 M. agrestis (cf. Fig. 2, B). The second and third molar 

 have 5 and 3 spaces respectively. 



Summarising, it may be said that the molars of M. 

 orcadensis resemble those of M. agrestis except that there 

 are 4 spaces in the second upper molar instead of 5. 



In considering all the features of the skull together, it is 

 clear that, except in regard to the teeth, M. orcadensis is 

 more closely allied to M. amphibius than to any other 



