664 MR. R. I. POCOCK ON THE EXTERNAL 



peculiarity is not so well marked in Allactaga and ScarturihS as 

 in Jacuhcs ; but tlie two common Egyptian Jerboas differ some- 

 what in this respect. In Scirtopoda orientalis this long bristle is 

 distinctly stouter and stiffer than the rest, and rises from a small 

 papillary i-oot, whereas in J. jacuhis the difference is considerably 

 o-reater, and the papilla from which it arises is much larger, 

 (Text-fig. 30, D.) 



In Pedetes the mystacial vibrissie are comparatively few in 

 number and short, although stout. A few longish superciliaxies 

 are present. The interi-amal tuft is apparently absent ; but the 

 genal is represented by two or three long vibrisste set high up 

 the cheek a little behind and below the posterior angle of the eye 

 as in the Hystricomorpha. 



By the characters mentioned above the genera may be arranged 

 as follows : — 



a. Rliinai'iuin ill defined, covered with hair except immediatelj' round 

 the nostrils, which are not visibly swollen and have no median 

 groove between them ; superciliary and genal vibrisste well de- 

 veloped ; mystacials stout and comparatively short Pedetes. 



a'. Rhinarium well defined, naked, nostrils with swollen rim and a 

 groove between them; superciliarj' and genal vibrissa few or 

 absent, uij'stacials long and slender for the most part. 

 I). Head narrow and low, murine in shape ; no median groove on 



upper lip; mouth with cheek-pouches (? in Sicista) Zapns, Sicista. 



b'. Head broad and high; upper lip. divided by philtrum, no cheek- 

 pouches Jaculus, Sch'topoda, Scartiirus *. 



The Ear. 



In Zapus the ear is moderately large and expanded, and arises 

 fi'om the head by a broad base which is not tubular. The anterior 

 edge is normally overfolded, and inferiorly about on a level with 

 the supratragus it is produced into a lamina which is normally 

 folded inwards out of sight. The lower edge of this curves into 

 the cavity of the ear and ceases on its floor. The tragus is 

 represented by a small movable lobe, and the antitragus by a large 

 tufted lamina which, when the ear is folded, projects forwards 

 and closes the lower portion of the cavity. The orifice is situated 

 just below and on the inner side of the cleej) intertragal notch. 

 (Text-fig. 31, A-C.) 



Miller describes the ear of Sicista loriger as " moderately large, 

 extending a little beyond tlie eye when laid forward, its outline 

 simple, ovate, its posterior border with large thickened lobe at 

 base, capable of completely closing the meatus, its anterior border 

 with minute though evident sub-basal notch and projection ; 

 both surfaces of ear densely clothed with short hairs ; basal lobe 

 cons^iicuously tufted." This description might have been taken 



* I have not seen a sufficient number of specimens ol Allactaga and other Asiatic, 

 genera of Jaculidse to know whether the cleavage of the upper lip is a constant 

 character in this group or not. 



