OF EXTINCT MUSCARDINE RODENT. 



211 



expanded. The infraorbital foramen opens anteriorly and the 

 outer wall of the infraorbital canal is very robust with a wide 

 base. The anterior palatine foramina penetrate for some distance 

 the palatal plate of the maxillae which forms the greater portion 

 of the palate. The angle of the mandible is perforated. Dental 

 formula i. ^, pm. m. f , molariform premolars and molar crowns 

 sub-quadrate in shape with low transverse ridges. Upper molars 

 with one large wide internal and two smaller external roots. In 

 the first and second lower molars the two posterior roots may be 

 confluent for the greater part of, or for their entire length ; the 

 last molar has two anterior and one large posterior root. Tibia 

 and fibula joined. 



Skull. — The skull is represented only by some few fragmentary 

 specimens none of which show the posterior portion, that is to say 

 behind the frontals. An isolated and imperfect auditory bulla 

 (B.M. Mil 671) was obtained which agrees in form and in the shape 

 and position of the meatus with the corresponding bone in Dyromys. 

 So far as available specimens show, the skull in general resembles 

 and may be compared with that of Eliomys, which for our present 

 purpose will be taken in a broad sense and to include Dyromys. 

 Even the smaller examples (those from Mallorca) are larger and 

 comparatively, as well as actually, more robust than E. lusitanicus, 

 which is the largest of the recent species of that genus. Viewed 

 from above, the nasals are seen to be practically flat and about 

 the same width throughout their length. The interorbital 

 portion of the frontals is wide and smoothly flattened and is 

 defined by sharp lateral edges ; a measurement taken at the 

 narrowest point is nearly half the antero-posteiior length of the 

 nasals in Hypnomys, whereas in E. lusitanicus it is not quite a 

 third. Anteriorly the frontals expand rapidly by a smooth 

 swelling and attain to a great width — about twice that of the 

 interorbital region — where they are joined by the nasals and 

 the nasal processes of the maxillae. This expansion is caused by 

 the very large size of the olfactory cavities (PI. I. fig. 14). There 

 is a fine but distinct ridge on the dorsal aspect of the maxilla at 

 the upper root of the zygoma from where the skull narrows 

 rapidly to form the snout. The premaxillse are robust, slightly 

 inflated dorso-anteriorly as in Eliomys, and deep dorso-ventrally, 

 the rostrum being stouter than in E. lusitanicus. The infra- 

 orbital region is not very well preserved in any of the Balearic 

 specimens, but sufficient is shown by two or three examples to 

 demonstrate that in this respect Hypnomys shows no close 

 resemblance whatever to either a typical Murine such as Ratlus 

 or to typical Sciurines such as Sciurus or Xerus. Though showing- 

 more general resemblance, this portion of the skull in the Balearic 

 genus still differs somewhat from that of any other of the 

 Muscardinidse with which I have been able to compare it ; in 

 some respects it seems to agree with that of Leithia, though 

 unfortunately all the anterior portions of skulls of this last in 



