Characters of scarturus and other jerboas. 669 



in EuchoreiUes, according to Sclater. there are only two, coire- 

 sponcling apparentl}^ to the median and outer of Scarturii,s ; in 

 Allactaga indica I can find only the median remaining, whereas 

 in Scirtopoda orientalis and J. jaculus all definite trace of them 

 seems to have disappeared, the sole of the foot in front of the 

 carpal pads being merely marked by integumental creases. As 

 in Sicista and Zapu,s, the carpal pad is double, the outer or ulnar 

 element being comparatively small, v\hile the inner or x-adial is 

 veiy large, especially in Allactaga indica, where it occupies 

 practically the whole of the posterior half of the sole. The 

 poUex is a mobile cylindrical process, covered above with a large 

 nail in Jaculus, Scirtopoda, Scarturus, and Allactaga, but in 

 Euchoreutes, according to Sclater, it is armed, like the other 

 digits, with a long claw. This author also described the digits 

 of Euchoreutes as long, but, judging from the figure, they are no 

 longer than in other genera of Jaculidfe. As in several Rodents, 

 notably the Squirrels, objects are held in the fore foot by folding 

 the four digits back upon the large carpal pad, which plays the 

 part, as it were, of a thumb. (Text-fig. 32, A.) 



The fore foot of Pedetes is short and broad, and has five well- 

 developed digits, all armed with long, stout, nearly straight claws 

 — the pollex being like the others, but shorter. The digital pads 

 are scarcel}^ defined ; and the under sides of the digits and the 

 short area of the sole distal to the carpal pads are naked and 

 granularly roughened. No trace of plantar pads remains. The 

 carpal pads are remarkable and, so far as I know, unique. They 

 are very large. The inner pad is an elevated thickened cushion, 

 beset on the summit with minute spicules. The inner pad is 

 laminate and normally fits closely against the outer pad, but is 

 independently movable like a valve, so that a deep space separates 

 the summits of the two pads. Its free edge, moreover, bears a 

 fringe of long hairs. This modification suggests that the carpal 

 pads are prehensile and aid in the grasping of food that is 

 gripped by the digits with their long claws. These claws are no 

 doubt also fossorial. (Text-fig. 35, A-C.) 



From the following summary of the characters of the fore foot 

 it will be seen that Pedetes stands apart from the other genera,. 

 It may be noted, however, that Sicista falls with the Jerboas 

 and not with Zapus :- — 



a. Fore foot with well-developed pollex armed with a claw as long as 

 on the other digits ; claws very long, stout, and straight ; carpal 

 pads separable and prehensile, the movaljle outer pad with fringe 



of long hairs Pedetes. 



a '. Fore foot with short pollex armed with a nail or slender claw ; claws 

 of digits 2 to 5 long or short, but slender and curved ; carpal pads 

 normal, confluent, the outer immovable and not fringed. 

 h. Foot elongated and narrow, digits unevenly spaced, 3 and 4 in 



advance of 2 and 5 Zapus. 



h'. Foot short and broad, digits 2 to 5 evenly spaced. 



c. Pollex armed with small claw (sec. Sclater) Ei(cli or elites. 



c'. Pollex armed with broad blunt nail Sicista, Jaculus, Scarturus, 



Scirtopoda, Allactaga, 



