680 MR. R. I. POCOCK ON THE EXTERNAL 



colour slightly different, I can find no difference between the two 

 in external characters to which I should attach generic value. 

 In dentition and cranial characters they are also much alike. 

 But the external genitalia of the male are profoundly different. 

 In my opinion these differences are of greater systematic im- 

 portance than the cranial and dental characters employed for 

 separating generically such forms as Jaculus jaculus and Dipus 

 sagitta*. I propose, therefore, to resuscitate the genus Scirtopoda 

 Brandt, separating it from Jaculus by the peculiar armature of 

 the glans penis. 



I a,m not in a position to give an opinion as to the suggested 

 identity betv/een S. mauritanicus and S. orientcdis ; but Duvernoy's 

 and Lereboullet's figures and description of the penis of mauri- 

 tanicus (Mem. Soc. Mus. Strasboiu^g, iii. no. 2, p. 48, pi. iv. fig. 12, 

 1842) show tliat that organ is of precisely the same nature as in 

 orientalis. The spikes on the penis appear, indeed, to be shorter 

 in onauritanicus than in orientalis, but that may be merely an 

 individual difference. 



Conclusions. 



The analytical keys published in the foregoing pages to show 

 the incidence of the genera according to the characters described 

 attest the isolation of Pedetes from the rest of the genera, and 

 thus bear out the prevalent opinion of the present day that that 

 genus is in no way related to the Jerboas and Jumping Mice. 

 Pedetes, therefore, need not be considered further in the present 

 connection. 



The keys also bear witness to the affinity nowadays admitted 

 to exist between the Jerboas and the Jumping Mice, but show 

 that the two may be sharply distinguished by the structure of 

 the hind feet. 



In 1901 Lyon (Proc. U.S. Nat. Mus. xxiii. p. 666), using 

 skeletal (mainly cranial and dental) characters, classified the 

 Jerboas and Jumping Mice as follows : — 



Family ZAPODiDiE. 



Subfamily Sminthin^ {SmintJnis, ? Eom.ys). 



,, ZapodiNjE {Za2jus, Napcmzapus, Eozapus^. 

 Family Dipodid^. 



Subfamily Dipodin^ {T)ipus, Allactaga, and probably Platycer- 

 comys). 

 „ EucHOREUTiiV^ (Eicchor elites). 



* I am aware that the use of soft parts for differentiating genera of Mammals 

 maj'_ be an annoj'ance to modern systematic maramalogists, who, following the 

 fashion set in the United States, like to woi'k from dried skins and skulls. But, 

 although the zoo-geographical and other results obtained from that method are of 

 great value and interest, 1 am sure that the sooner the swing of the pendulum carries 

 us back to the method in vogue thirtj' years ago of working from fresh or spirit- 

 preserved material, combined with skins, the better it will be for the science of 

 mammalogj^ 



