236 . MR. R. I. POCOCK ox THE 



c. Disc comparatively small, its width about half the length of 

 the shaft, the tip of the shaft projecting as a process be- 

 neath it mongolicus. 



c'. Disc verj^ wide, its width almost equal to the length of the 

 shaft, the apex of which forms no projection beneath it in 

 front — leursi. 



In Gynomys ludovicianus the glans penis is short, its proximal 

 two-thirds being stout and subcylindrical and its distal third 

 forming a quite narrow terminal process sharply defined from 

 the thicker portion. The orifice lies on the right side close to 

 the base of the narrowed end. The baculum, measuring 4 mm. 

 in length, lies in the narrowest portion and reaches its apex. 

 It is broader at the base and tip than in the middle and is 

 slightly asymmetrical. Its upper edge is very slightly concave, 

 its lower edge mesially geniculate, the apex being irregularly 

 denticulated. (Text-figs. 25, I ; 26, K-M.) 



In Marmota marmota the glans penis is shaped very much 

 like that of Cynomys, but is relatively a little shorter. The 

 orifice opens similarly on the right side at the base of the 

 narrowed terminal process and the baculum, measuring only 

 7 mm., and lying in the narrowed piece is a slightly asym- 

 metrical bone with expanded base and expanded irregularly 

 denticulate apex. It is not quite alike in two specimens 

 examined, and I am unable to affirm an 3^ character apart from 

 size by which it may be distinguished from the baculum of 

 Cynomys. (Text-figs. 25, K ; 26,' N, 0.) 



It may be recalled that Tullberg many" years ago described 

 the glans penis of Marmota [Aj^ctomys'] as very small and asym- 

 metrical, with the opening on the right side behind the tip, which 

 carries a small baculum. The male genitalia of Cynom.ys he 

 described as like those of Marmota ; but, what is more interesting 

 still, he declared the male genitalia of Tamias to be also very 

 similar to those of Marmota. 



6. The Suhfamilies of Sciuridce. 



For the following grouping of the genera of n on- volant 

 Squirrels, constituting the Sciuridae, I take the glans penis and 

 the baculum as supplying characters of primary value. It may 

 be objected that these characters appl}?- only to one sex ; but I 

 do not think it can be doubted that corresponding differences 

 occur in the females and merely await discovery. The baculum 

 has been examined either by Mr, Thomas or myself in all the 

 principal genera, and the penis by Tullberg and myself in a 

 considerable number of them. As subsidiary characters I have 

 used the ears and feet, leaving alone crapial and dental 

 characters, the study of which by Thomas, Forsyth Major, and 

 many American authors has led to no very satisfactory result 

 apart from the steady but unavoidable and convenient multi- 

 plication of genera and subgenera. 



