192 Proceedings of the Biological Society of Washington. 



Color of type and 4 topotypes (Sept. 28 to Nov. 4): upper parts dull 

 russet, brightest on crown, palest on cheeks and rump; ears dark brown 

 like underfur of back ; lower parts clear drab or dull buft'y gray, overhair 

 and underfur the same shade; sides and feet darker drab. Usually a 

 trace of bright chestnut about the anus, and in the type and one topotype 

 some chestnut on the hind feet. A topotype young of the year (Sept. 

 28) is slightly duller and darker than the adults. Two very small young 

 (April 3 and 5) from the Rio Grande at Brownsville are practically the 

 same color throughout as the adults, as is also a good specimen from 

 Four Mile Run, Va., supposed to be one of the Brownsville beaver that 

 escaped from the Washington Zoological Park. A half-grown specimen 

 from Costilla River (an eastern affluent of the Rio Grande in northern 

 New Mexico) taken August 23, is slightly darker and richer colored than 

 the type and is evidently grading toward canadensis or frondator. 



Cranial characters. — Compared with skulls of typical canadensis from 

 York Factory and Oxford House, Manitoba, the skulls of this form are 

 relatively short, wide and high, with more spreading zygomatic arches, 

 shorter, wider nasals and rostrum, and higher, narrower occiput. Most 

 of these characters are tending toward those of frondator and texensis, 

 from both of which they differ however in details sufficient for ready 

 recognition. From frondator the skull differs in heavier, deeper jugal, 

 lower occiput and wider ex-occipital condyles. From texensis the skull 

 differs in short, oval nasals, in narrower interorbital constriction and 

 numerous other details. 



Measurements. — Type, $ ad., total length, 1070; tail vertebrae, 400; 



.hind foot, 174. Weight, 47 lbs. Ad. c? topotype (No. 96,525), 1020, 



300, 180. Skull of type, condylobasal length, 136; zygomatic breadth, 



101; length of nasals, 49; width of nasals, 25; mastoid breadth, 66; 



height of occiput, 40.3; alveolar length of upper molar series, 30.3. 



Castor canadensis michiganensis subsp. nov. 



WOODS BEAVER. 



Type from Tahquamenaw River (rive miles above falls), Luce Co., 

 Michigan, 9 adult, No. 170,561. U. S. Nat. Mus., Biol. Survey Coll., 

 collected Sept. 20 by Clarence Birdseye. Collector's number, 1270. 



General rharacters. — Size medium or small, colors very dark, ears and 

 feet black ; skull short and quadrate. 



Color of type in early winter pelage: upperparts dark umber brown, 

 brighter, almost mahogany brown on head and cheeks; ears and feet and 

 nose black ; lowerparts rather darker than upperparts, with blackish on 

 breast and flanks. Quarter-grown young of same date and place duller 

 and darker than type. 



Skull relatively short and wide with abruptly spreading zygomatic 

 arches; rostrum short and less tapering than in canadensis; nasals more 

 quadrate, abruptly constricted posteriorly; occiput high and narrow 



