668 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxiii. 



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TuLLBERG, Tycho. Uebef das System der Xagethiere, 1899, pp. 181-195. 



Wagner, J. A. Gruppirung der Gattungen der Xager in natiirlicher Familien. 



Archiv fiir Xaturgeschichte, Berlin, 1841, p. 111. 

 Wagxer, J. A. Schrebers Saugthiere. Fortgesetzt von J. A. Wagner, III, 1843, 



pp. 274-295. 

 WATEKHorsE, G. R. Observations on the Rodentia. Magazine (if Xatnral Historv, 



III, 1839, pp. 60-91, 186-188. 

 WiNGE, Herluf. Jordfundne og nulevende (inavere (Rodentia) fra Lagoa Santa, 



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 Zittel, K. a. Handbuch der Palteontologie. Part I, IV, 1893, pp. 526-527. 



EXPLAX'ATIOX OF PLATES. 



All figures one and a half times natural size. The letters on the plates have the 

 following significanee: 



Sq, squamosal. N, navicular. 



m, mastoid. Cu, cuboid. 



So, supraoccipital. Ec, Mc, and Ic, external, midille, and 



C, calcaneum or os calcis. internal cuneiform. 



^•1, astragalus. 



Plate XXV. 



Fig. 1, lateral view of skull of Zapus. 



2, lateral view of skull of Euchoreutes, redrawn to scale from Sclater's figures 



in Proc. Zool. Soc. Lond., 1890, p. 611. Compare with Zapus and Smuithus 

 and note similarity of the zygomata. 



3, lateral view of skull of Sminthus. 



4, lateral view of skull of Dipus. 



5, lateral view of skull of Alactaga. 



Plate XXVI. 



Fig. 1, ventral view of skull of Zapus. 



2, ventral view of skull of Euchoreutes, redrawn to scale from Sclater's figures 



in Proc. Zool. Soc. Lond., 1890, p. 611. Xote the similarity of the ventral 

 view with the same aspects of Dipus and Alactaga. 



3, ventral view of skull of Sftunlhus. 



4, ventral view of skull of Dipus. 



5, ventral view of skull of Alactaga. 



Plate XXVII. 



Fig. 1, left hind foot of Zapus, dorsal view and internal lateral view of the tarsal 

 bones. 



2, left hind foot of Alactaga, dorsal view and internal lateral view of the tarsal 



liones. The pre-tarsal part is drawn from a specimen in the American 

 INIuseum of Natural History; the tarsal bones are filled in from a dissected 

 tarsus taken from a skin in the V. S. National INIuseum. 



3, left hind foot of Dipus, dorsal view and internal lateral view of the tarsal 



bones. Rudiment of the fifth metatarsal mav be seen. 



