452 MB. W. E. DE WIIfTON ON A NEW RODENT [May 17, 



The general form of the skull (Plate XXXV. figs. 1-4) more 

 nearly resembles that of Idiurus than Anomalurus, and in the 

 proportion and form of both incisors and molars (Plate XXXV. 

 figs. 6, 7) there is still nearer resemblance to the former. It is 

 impossible at present to compare the skull directly with that of 

 Idiurus, as tiie Museum does not contain a specimen of that genus ; 

 comparison will therefore be based upon the figures of Idiwus 

 macrotis given by Mr. G. S. Miller, Proc. Biol. Soc. Washington, 

 xii. p. 75, for March 1898. 



The most striking differences are found in the palate, the zygo- 

 mata, and the supraorbital region of the frontal bones ; in these 

 particulars the skull is also wholly unlike that of Anomalurvs. 



Taking these differences in the above order, in the animal under 

 notice, in front of the molars the palatal aspect of the maxillsB is 

 of uniform width, absolutely horizontal, with abrupt lateral edges ; 

 these straight lines are not found in the skull of any other rodent. 

 The anterior (lower) root of the zygomatic process of the maxilla 

 is set diagonally across the corner of that bone, springing abruptly 

 from immediately behind the suture with the premaxilla, and is 

 thus placed nearer to the incisors than to the molars (a character 

 in which it appears to agree with Idiurus, and in a less degree 

 resembling the form found in Fedetes) ; the process is narrow, solid, 

 and rod-like, ascending and diverging to meet the malar, with 

 which bone it forms an obtuse angle, and sending out only a very 

 short spur-like process upon which the malar rests ; it continues 

 then only to form half, or the inner margin, of the frame of the 

 anteorbital foramen ; the malar sending out a long ascending 

 process, luhich joins the lachrymal, forms the posterior portion of 

 the upper root of the zygomatic ai'ch, or the anterior wall of the 

 orbital cavity. 



The malar is of unusual depth ; tbe lower edge is quite straight, 

 forming an angle posteriorly. The squamosal process is unusually 

 developed, extending about halfway along the upper side of the 

 arch, and so forming the ■postorhital ascending angle, a character 

 with which I can find no parallel. 



The frontal bones are very unlike those oildivrus or Anowalurvs 

 in the total absence of any projecting ridges or postorbital processes, 

 agreeing in this respect with the Myoxidce. 



The auditory bullae are very small. The hack of the palate and 

 the pterygoids throughout are \<ivy like those of Anomalurus ; the 

 ectoptery golds are absent or rudimentary as in the two allied 

 genera. The palate is narrow and peculiarly uniform in width 

 along its whole length ; from the palatal to the incisive foramina 

 there are two grooves forming a median rounded ridge along the 

 centre of the palate. The external view of the incisive foramen 

 (there is but one) is little more than a narrow slit: possibly the 

 true formation is a still further development of the sinus or pit 

 found in Pedetes, in which the foramina are placed ; in any cnse 

 this formation would probably only be the result of the deepening 

 of the facial portion of the skull, to give strength in gnawing. 



