Key to the Skulls of North Dakota Mammals

1. One upper incisor on each side...............................................2
   Two upper incisors on each side..............................................3

2. Greatest length of skull more than 15mm......................Lasiurus cinereus
                                                                        Hoary Bat
   Greatest length of skull less than 15mm......................Lasiurus borealis
                                                                          Red Bat

3. Four upper molariform teeth on each side......................Eptesicus fuscus
                                                                    Big Brown Bat
   Five or six upper molariform teeth on each side..............................4

4. Five upper molariform teeth on each side.............Lasionycteris noctivagans
                                                                Silver-haired Bat
   Six upper molariform teeth on each side (Myotis —— these species
     are difficult to separate).................................................5

5. Length of upper tooth row 6mm or longer..........................Myotis evotis
                                                                Long-eared Myotis
   Length of upper tooth row less than 6mm......................................6

6. Occipital condyles usually elevated above level of auditory
     bullae (Fig. 12)...............................................Myotis volans
                                                               Long-legged Myotis
   Occipital condyles usually not elevated above level of auditory
     bullae (Fig. 13)...........................................................7

7. Interorbital breadth usually 4mm or more (Fig. 14)............Myotis lucifugus
                                                              Little Brown Myotis
   Interorbital breadth usually less than 4mm...................................8

8. Greatest length of skull usually more than 14.6mm................Myotis keenii
                                                                    Keen's Myotis
   Greatest length of skull usually less than 14.6mm................Myotis leibii
                                                              Small-footed Myotis