CHARACTERS OF SCARTURUS AND OTHER JERBOAS. 663 



when digging its burrow " (Mamm. Egypt, p. 304). The rhinarium 

 when thus partially concealed also contracts very perceptibly, the 

 nostrils are approximated and a,ssume a more vertical appearance, 

 and the philtrum is obliterated by the median juxtaposition of 

 the two halves of the upper lip. This device probably serves to 

 exclude fine blown sand, as well as the soil when digging is in 

 operation. (Text-fig. 30, B, 0.) 



The rhinarium of Pedetes is quite unlike that of Zapus and 

 Jaculus. It is covered above and in front with fine short hair ; 

 but the nostrils, which are elongated and appear to be valvular, 

 are surrounded by a narrow rim of naked skin. The median 

 portion of the rhinarium below the nostrils in front is angled, 

 but there is no trace of groove or philtrum dividing the deep 

 upper lip, which is covered uniformly with longish hair (text- 

 fig. 30, E). 



Both in Zapus, Jaculus, Scirtopoda, and Scarturus, the mouth 

 is provided with well-developed palatal and lingual lobes jutting 

 inwards from the cheek. The palatal lobes meet along the middle 

 line of the palate, but are separable and do not fuse in the 

 middle line, the epithelium of the palate being smooth. The 

 lingual lobes, which are long, meet in the middle line over or 

 in front of the tongue, forming a secondary floor to the mouth. 

 Zapus is provided with cheek-pouches opening just inside the 

 corner of the mouth. The Jaculida3 are without them, and, so 

 far as I am aware, they have never been recorded in Sicista. 



In connection with the mouth, reference may be made to the 

 presence in some genera of grooves on the incisor teeth. Their 

 incidence is remarkable and puzzling. They are absent in Sicista, 

 the least specialised genus of the group ; but are present in Zapus, 

 which seems to be much more neai"ly akin to Sicista than it is to 

 any genus of Jaculidae. Within the Jaculidte, the grooves are 

 present in Dipus, Jaculus, Scirtopoda, and Cai'diocranius ; absent 

 in Allactaga, Scarturus, Etichoreutes, and Pygeretmus. Their 

 presence, as recorded by Satunin, in Gardiocranius — a genus 

 resembling Pygeretmus in possessing five toes on the foot and a 

 specialised broad lanceolate tail — suggests that the character has 

 no great systematic value. 



Facial Vibrissce. 



The mystacial vibrissas are well developed in Zapus. One or 

 two long superciliary vibrissse are also present ; but in the long 

 hairs clothing the cheek I failed to find the genal tuft. The 

 inteiTamal is represented by two very fine vibrisspe in one example. 

 In the Jaculidpe the interramal tuft is apparently absent, 

 and the superciliaries and genal tufts are of inconstant occur- 

 rence, and represented at most by one or two fine vibrissse each. 

 But the mystacials are well developed, one of them on each side 

 set low down being stouter and longer than the rest. This 



