The Fur Animals of Louisiana 195 



subspecies would be of little value in identifying specimens, 

 but, realizing that such a key would have important uses 

 as a means of ready reference to characters, and in other 

 ways, he prepared the following, which is reproduced from 

 his "Systematic Synopsis of the Muskrats," published in 

 1911: 



Key to Adult Muskrats in Fresh Pelage 



Size large; hind foot averaging over SO mm. 



Coloration darker; blackish or blackish brown. 



Skull with high, sharp interorbital ridge; nasals broadly spat- 

 ulate anteriorly (Puget Sound region and Rocky Moun- 

 tains) osoyoosensis 



Skull without specially developed interorbital ridge. Largest 

 in the genus; tooth row averaging over 17 mm.; coloration 

 blackish (Atlantic coast, Delaware Bay to North Carolina). 

 Black phase of macrodon 



Size less; tooth row averaging under 17 mm.; coloration dark 



brown ( S. E. Canada and N. E. United States) sibethicus 



Coloration lighter ; reddish brown or grayish brown. 



Interpterygoid fossa narrow, with borders nearly parallel 

 I Western Oregon) occipitalis 



Interpterygoid fossa, much widened posteriorly, upperparts 

 grayish brown, with darker dorsal area (Great Basin 

 region ) mergens 



I'nderpaits bright reddish brown; size very large (Atlantic 

 coast, Delaware Bay to N. C). Normal phase of. . . .macrodon 



Size small ; hind foot averaging less than 80 mm. 

 Coloration dark ; black or blackish brown. 



Skull with high, sharp interorbital ridge. 



Zygomata broadly spreading anteriorly (Alaska and N. W. 



British America) spatulatus 



Zygomata not broadly spreading anteriorly. 



Hind foot averaging 75 mm.; colors darker with more rusty 



tinge ( Keewatin and eastern Saskatchewan) albus 



Hind foot averaging less than 70 mm. ; colors lighter with 



little rusty tinge (Alaskan Peninsular) zalophus 



Skull without distinct interorbital ridge. 

 Coloration glossy blackish. 



Tail long (averaging over 260 mm.); skull large (Labra- 

 dor and Ungava ) aquilonius 



Tail short (averaging less than L'30 mm.) ; skull small and 



weak (Newfoundland) obscuru.s 



Coloration dull blackish brown; under parts dark (coast region 



of Louisiana ) rivalicius 



Coloration pale; reddish or pale brown. 



Larger (tail averaging 210 mm.; hind foot over 7:? mm.) (great 



Plains region) cinnamominus 



Smaller (tail averaging less than 205 mm.; hind foot less than 

 70 mm.). Upperparts cinnamon rufous (Colorado River east 

 to Rio Grande in New Mexico [now in Imperial Valley, Cali- 

 fornia]) pallid im 



L'pperparts Vandyke brown (Pecos Valley, Texas, and New 

 Mexico ) Hpensia 



