682 THE EXTEENAL CHARACTEHS OF SCAKTUEUS. 



upper incisor teeth and the closed or open canal for the antorbital 

 nerve. I am not aware whether these are constant differences. 



Adopting Lyon's classification with the modifications above 

 mentioned, the families and subfamilies of Jumping Mice and 

 Jerboas will be as follows : — 



I. Family Zapodid^e, 



1. Subfamily Sicistin^ *= SMiNXHiNiE (Sicista). 



2. ,, Zatodinje (Zapus, Napceozapus, Eozapus). 



II. Family Jaculid^ or Dipodid^. 



1. Subfamily Jaculin^ or Dipodin^ (Jaculus, Scirtopoda, 



Dipus, /Scarturus, AUactaga, Alactagulus). 



2. ,, PYGEEETMiNJi; {Pygeretmus, Gardiocranius). 



3. „ EucHOEEUTiNiE {Euchoreutes). 



The chief distinguishing characters of the Zapodidse and 

 Jaculidse and of the Sicistinse, Zapodinse, and Euchoreutinse may 

 be found in Lyon's paper. Those of the Pygeretminse are stated 

 above. With regard to the Jaculinse, the genera which appear 

 to me to be admissible, though there may be others, may be 

 distinguished as follows : — 



a. Five or four toes on the hind foot; incisors ungrooved ; antorbital 

 nerve-canal open above. 

 h. Five toes on foot, hallux present. 



c. Small upper premolar retained AUactaga. 



c'. Small upper premolar lost Alactagulus. 



v. Four toes on foot, hallux lost (skull and dentition as in 



AUactaga) Scarturus. 



a'. Three toes onlj' on hind foot ; incisors grooved ; antorbital canal 

 closed above (? always). 



d. Small upper premolar retained ; mastoids less inflated Dipus. 



d'. Small upper premolar lost ; mastoids much inflated. 



e. Glans penis without spikes, with insunk scaly armature Jaculus. 



e'. Glans penis with a pair of large erectile spikes and spinous 



armature Scirtopoda. 



* See Miller, Cat. Mamm. Western Europe, p. 536 (1912). 



