Key to the Skulls of North Dakota Mammals

1. Greatest length of skull usually more than 20mm; two lower
     incisors on each side (Fig. 8)............................Blarina brevicauda
                                                               Short-tailed Shrew
   Greatest length of skull usually less than 20mm; one lower
     incisor on each side.......................................................2

2. Three of the five upper unicuspids clearly visible in lateral view
     (third and fifth barely, if at all, visible)(Fig. 9).........Microsorex boyi
                                                                      Pigmy Shrew
   Four and usually all five upper unicuspids clearly visible in
     lateral view (Fig. 10).....................................................3

3. Maxillary breadth less than 4.6mm; condylobasal length of skull
     14.6 - 16.9mm (Figs. 8, 11)...................................Sorex cinereus
                                                                     Masked Shrew
   Maxillary breadth more than 4.6mm; condylobasal length of
     skull 17.8 - 19.1mm...........................................Sorex arcticus
                                                                     Arctic Shrew