284 MR. R. F. TOMES ON A COLLECTION [JuDC 25, 



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Length of the incisive foramina 4 



of the palate 4 



Breadth of palate between two front molars. . 1^ 



of palate between two posterior molars 2 



Length of lower jaw from point of incisors to 



condyle 1 



Depth from coronoid process to the angle. ... C 



22. Hesveromys ? 



Closely resembles H. leucopus \ but the cranium is a little narrower, 

 and the general colour of the fur much more rufous. 



23. Hesperomys 1 



24. Reithrodon longicauda, Baird. 



25. Reithrodon MEXicANA,DeSaussure,Rev.Zool.l860,p.l09. 

 25. Hesperomys (Myoxomys) salvini. 



Since the publication of my last notes on Mammals collected by 

 Mr. Fraser, I have had occasion to examine anew the species of 

 Hesperomys mentioned therein, and have compared them with a 

 more extended series of species. The result is a considerable modi- 

 fication of the classification which I then adopted. It is not my 

 intention to enter now into the distinction of the several groups of 

 Hesperomys ; but it is necessary that I should define one of them, 

 for the purpose of afterwards describing a remarkable species con- 

 tained in the present collection. 



Subgen. Myoxomys. 



General form much resembling that of Myoxus ; muzzle short, 

 but not swollen ; eyes large ; ears variable in size, roundish, and not 

 concealed by the fur ; feet very short and broad, toes differing from 

 each other in length only ; j)alms and under surfaces of toes thick 

 and fleshy, with their tubercles well developed ; nails very short ; 

 tail fully as long as the body, sometimes much longer, of nearly uni- 

 form size, and suffused with hairs, which are most abundant towards 

 and at the extremity ; fur short, fine, and without gioss ; the colours 

 of the upper and under parts of the body divided by a well-marked 

 line. 



Skull broad, its nasal region short ; zygomatic arches much ex- 

 panded ; space between the orbits broad, and bounded by a well- 

 developed supra-orbital crest ; ante-orbital foramen large, the bony 

 plate which encloses it very narrow, so that it opens forward and not 

 at all upwards ; palate extending posteriorly only to the boundary 

 of the molar series ; condyloid process of the lower jaw considerably 

 longer than either the coronoid or descending processes. 

 Ex. Myoxomys salvini, n. sp. (most typical species). 

 M. latimanus. Tomes. 

 M. bicolor, Tomes (least typical species). 



