666 MR. R. I. POCOCK ON THE EXTERNAL 



Scarturus, wliich has a sboi't snout, they surpass it by a little. 

 In Allactaga inclica they reach about to the end of the muzzle, 

 and in most species assigned to this genus they appear, judging 

 from Lichtensteiu's figures, to re;ich well beyond the eyes at all 

 events. In Scirtopoda orientalis they overlap the eyes by a little ; 

 in J. jaculus they just cover them. In other species figured by 

 Lichtenstein they are as short n,s in the typical species or shorter. 

 But despite their length they all appear to be similarly con- 

 structed. They are more or less tubular at the base, the orifice 

 being sunk deep down within the cavity. There is no trace of 

 tragal lobe or antitragal flap, such as are seen in Za.pus and 

 JSicista; but just v/ithin the anterior edge, on a level with the 

 supi'atragua, there is a delicate membranous lamina descending, 

 as in Zapus, into the tubular basal portion and normally folded 

 in out of sight. The lower end of this lamina curves backwards 

 and inwards, and just inside its lower end there is a deep ca.vity 

 bounded above by the anterior end of the supratragus, which is a 

 slender delicate ridge running backwards towards the posterior 

 edge of the ear, exactly as in Zapus. The orifice is situated 

 a little below this anterior cavity, and is separated from it by a 

 thickening. There are minor differences in the structure of the 

 ear which may prove to hfl.ve systematic importance, but my 

 material is not sufficient in quantity to establish the point. In 

 Scirtopoda orientcdis, for instance, the anterior infolded lamina 

 is lai'ger than in Scarticrus, and the area round the auditory 

 orifice is more swollen. In Scarturus, on the other hand, the 

 lower end of the passage leading to the anterior pit is much more 

 swollen than in S. orientalis., and the tubular portion of the ear 

 is provided Avith a fine delicate lamina ascending from a point 

 behind the auditory orifice up to the position of the aborted 

 antitragus. This is not so noticeable in *S'. orientalis. Sclater's 

 brief description of the ear of Euchoreutes contains nothing to 

 suggest any difference between that genus and the three I have 

 examined in the structure of the organ in question. (Text- 

 fig. 31, D, E.) 



From what has been said above it will be clear that the kinship 

 claimed to exist between Zapus and the Jaculidse on cranial 

 grounds is completely boi-ne out by the ear. The ear of the 

 Jaculidfe may be regarded as a derivative of the type seen in 

 Zapus, specialised by its more tubular base, with which the dis- 

 appearance of the tragus and antitragus is correlated. In the 

 Jaculidas, too, the anterior basal pit is deeper and its inferior edge 

 is closer to the auditory orifice. 



The ear of Pedetes is very different from those described above, 

 altliough in its tubular base and its length it recalls in appear- 

 ance the ear of some Jaculidse. It shows, however, in its posterior 

 border behind the tip, a shallow but long emargination, similar 

 to the emargination so common in many of the Hystricomorpha. 

 The anterior edge is not overfolded and there is no inturned lamina 

 at the base. There is no antitragus, but from the inner side of 



