636 



MILLER 



Skull. — In size and general appearance the skull of Mus defua 

 closely agrees witli that of Mks riitilans. The rostrum, however, is 

 narrower, and the dorsal profile of the nasals is much less distinctly 

 bent downward near middle. Antorbital foramen barely more than 

 half as wide as in Mus rutilans^ its contraction especially noticeable 

 below middle. The depression which extends forward on side of 

 rostrum from antorbital foramen above root of incisor is smaller and 

 less well defined than in Mus rutilans. On the lower side of the 

 skull a few slight differences may be seen, some of which may prove 

 to be mere individual vai-iation. The incisive foramina are narrower 

 than in Mus rutila7is though of about the same length. The inter- 

 pterygoid space on the contrary is wider in the Liberian animal. 

 Audital bullffi like those of M71S rutilans but slightly smaller. Man- 

 dible with narrower angular process and shorter coronoid process than 

 in Mus rutilans. 



Teeth. — Though the toothrow is no longer, the individual teeth of 

 Mus defua are broader and heavier than those of M. rutilans. Aside 

 from their difference in general form, the maxillary teeth of ]\Ius defua 

 are peculiar in the greater disproportion between the central and lateral 

 tubercles ; the former are actually larger than in Miis rutilans while 

 the latter are smaller and less definite in outline, particularly those on 

 outer side. First molar with two well-developed tubercles on inner 

 side, slightly larger than the corresponding ones in Mus rutilans and 

 more posterior in situation. On the outer side there is a minute an- 

 terior tubercle smaller and further forward than in Mus rtitilans, and 

 a median tubercle of about the same size as in the latter. The pos- 

 terior outer tubercle, small but well developed in Mus rtitilafts is here 

 reduced to a mere trace on the outer side of the third median tubercle. 

 The arrangement of the tubercles in the other maxillary teeth and in 

 those of the mandible is essentially as in M71S rzitilans. 



Measurefnents. — External measui'emcnts of type: total length 310; 

 tail vertebras 187.5; Ji'ii<^l foot 26.7 (25); ear from meatus 16; ear 

 from crown 12; width of ear 12. 



Cranial measurements of type : greatest length 32 ; basal length 

 27; basilar length 24.4; palatal length 13.6; palatal width between 

 anterior molars 2.S; diastema 8.8; length of incisive foramen 6.4; 

 combined %vidth of incisive foramina 2.4; length of nasals 11.6; 

 greatest conil)iiK'(l breadth of nasals 3; zygomatic breadth 16. S; mas- 

 toid breadth 12; interorbital breadth 5.2 ; breadth of braincase above 



relatively to the width of the rings, and therefore actually much longer than in 

 Mus defua. 



