172 Field Museum of Natural History — Zoology, Vol. XI. 



Skulls of Muridce. (About natural size.) 

 I, Mus musculus; 2, Epitnys norvegicus; 3, Perotnyscus leucopus; 4, Oryzomys palusiris: 5, NeO' 

 tomaf. illinoiensis; 6, Evolomys gapperi; 7, Microtus pennsylvanicus; 8, Fiber zibethicus; 9, Synapto- 

 mys cooperi. 



