})(> OBSERVATIONS ON THE RODENTIA. 



of the Spermophili (if not all) it is very small, and it is also 

 small in the genus Geosciurus of Dr. And. Smith, (which I have 

 no doubt is the same as the genus Xerus of Hemp and E hr.) 

 The palate is proportionally larger in the Sciuridae than any 

 other Rodents. It almost always extends considerably be- 

 yond the last molars. In Sc. Prevostii however, the palate 

 terminates in the line of the hinder portion of the last molar, 

 and in Sc. maximus and Sc. Leschenaultii it terminates rather 

 within this line. The position, combined with the small size 

 of the ant-orbital foramen, will also serve to distinguish the 

 Sciuridce. The genus Castor, in the character of the ant- 

 orbital foramen, makes the nearest approach to the present 

 family ; here however, this opening is not so low down. 



The general form of the skull in the true SciuridaB is short 

 and rounded, the cranial portion is very large, and the nasal 

 portion short. In the genus Arctomys the nasal portion is 

 proportionately larger, and the cranial smaller. Here the 

 interorbital portion of the skull is considerably contracted, as 

 we also find the same part in the larger species of Pteromys, 

 these however have the short nasal bones, as in the genus 

 Sciurus. In Sc. palmarum, and in the genera Spermophilus 

 and Geosciurus (Sci. erythropus 1 ), the skull is considerably 

 elongated and somewhat ovate, the nasal bones are longer 

 than in the true squirrels. The animal last named offers ma- 

 ny peculiarities in the form of the cranium, it is not however 

 my intention to enter into detail at present ; I will merely no- 

 tice one, viz., the horizontally compressed form of that por- 

 tion of the zygomatic arch which forms the lower boundary 

 of the orbit : a character in which it differs from all the other 

 Sciuri examined by me, but to which I find an approach in the 

 skull of a species of Spermophilus, (Sp. Franklinii). 



The genera and subgenera contained in this family the skulls of which 

 I have examined, are — Pteromys, Sciuropterus, Sciurus, Macroxus, Tamia, 

 Geosciurus, Spermophilus, and Arctomys. 



(To be continued.) 



1 1 am indebted to Dr. Richardson for the loan of the skull of this spe- 

 cies, and also of the crania of several other rodents, which have been of great 

 service to me. 



