OF THE BEAVER AND OF SOBIE SQUIRRELS. 1205 



workers with more and better material, I subjoin the following 

 table : — 



a. Metatarsal area liairj^, without pads Sciii,ropte7'us, Glaucomys. 



a'. Metatarsal area partially naked with the inner pad 

 at least retained. 



h. Inner metatarsal pad confluent with plantar pad ; 



pollex practically suppressed, without nail Fetaurista albiventer. 



h'. Inner metatarsal pad distinct from plantar pad ; 

 pollex as in typical Sciuridre. 



c. Outer metatarsal pad retained ^oglaucomys fimhriatus . 



c' , Outer metatarsal pad lost. 



d. Inner metatarsal pad elongate Fetinomys fuscocapilhis. 



cZ'. Inner metatarsal pad oval JBelomys pearsoni, Mylo- 



petes alboniger. 



h. Feet of the Beaver (Castor). 



Apart from minor difiei'ences, the fore foot of Castor fiber 

 differs from that of the Beiuridss and Petauristidse in two 

 important points, the presence of a well-developed pollex and the 

 indistinctness of the lol)es of the plantar pad. The digits are 

 short, with roughened but not well-defined digital pads ; the 

 third is the longest, a little exceeding the fourth, the second and 

 fifth being shorter, and the first, or pollex, the shortest of all. 

 All are armed with long, wide, blunt, slightly curved claws, that 

 of the pollex being a little narrower, sharper, and more curved 

 than the rest. The plantar area is granularly reticulated, and 

 the lobes of the plantar pads are obscurely represented by mobile 

 folds of thickened granular skin, hardly alike in any two 

 specimens or even on the two feet of an individual. Only some- 

 times are the thickenings arranged so as to indicate the three 

 main plantar lobes present in all the Sciurid^e. Behind the 

 plantar area there are two v/ell-developed elongated carpal pads. 

 The inner at the base of the pollex is the smaller, and is hard, 

 smooth, and grooved except at its distal end. The outer pad is 

 much longer and wider, and extends considerably further up the 

 wrist proximally. The comparatively wide space between these 

 pads is occupied by thickened granular skin, which on the 

 admedian side of the inner carpal pad, and a little in front of it, 

 forms sometimes a lobate thicKening, which may represent the 

 inner or pollical element of the plantar pad, which should be 

 present with a well-developed pollex, but which is absent in all 

 the Sciuridse, where the pollex is little more than a vestigial 

 remnant. There is a rim of naked skin behind these carpal pads ; 

 but on the inner side of the wrist the hairs are directed obliquely 

 towards the middle line, in a crest overlapping the posterior 

 portions of the pads. There are no carpal vibrissee, which are 

 present in all Sciuridse. (Text-fig. 58, A.) 



The hind foot greatly surpasses the fore foot in size, far more 

 so than in any member of the Sciuridje. This is mainly due to 



Proc. Zool. Soc— 1922, No. LXXX. 80 



