Size large; bodj' heavy, bulky; three upper and under anterior 

 molars very small with but a single root and frequently deciduous; 

 fourth upper premolar lacks inner tubercle supported by a separate 

 root; fourth premolar larger than those before it, the upper one has 

 three roots, the lower one two; skull elongate, feet broad, toes 

 armed with long, somewhat curved claws; non-retractile; palms and 

 soles naked. Tail exceedingly short; ears erect, rather short, 

 hairy. 



A. Thalassarctus. 



Neck elongate; upper tubercular molar elongate; palate broad, 

 suddenly contracted behind last molar; posterior nasal aperture elon- 

 gate, narrow; sides arched, contracted in middle. Soles of feet hairj', 

 with small bald pads. Forehead nearly on line with nose. 



467. maritimus. {C'rsus), Desm., Mamm., 1820, p. 165. 

 Tj/c- locality. Arctic region. 



Geogr. Distr. Arctic regions of the world. 



Genl. Char. Head elongate; molars small and narrow. 



Color. White at all seasons; sometimes portions of the pelage 

 tinged with \ellow or saffron. 



Measurements. Total length, 2500-3300. Skull: greatest length, 

 407; greatest width, 245. Dimensions vary greatly among indi- 

 viduals. 



B. Ursus. 



Forehead concave, rounded; brain case swollen; nostrils ovate 

 covered by a lid; nose longer than broad; palate flat; base of toes 

 beneath covered with hair. 



468. middendorffi. {Ursiis), Merr., Proc. Biol. Soc. Wash., 1S96, 



p. 69. pi. Iv, figs. 2 and 3; pi. v, fig. 2; pi. vi, fig. 2; p. 70, 



fig- 7- 



Type locality. Kadiak Island, Alaska. 



Geogr. Distr. Kadiak Island, Alaskan Peninsula, Kenai Penin- 

 sula, Prince William Sound, Sushitna and Kuik River regions, and 

 the Alaskan Mountains. 



Genl. Char. Size large; frontal region in male considerably 

 elevated, arched and rather narrow; postzygomatic part of skull 

 very short. 



Color. The color varies greatly among individuals, being of 

 various shades and combinations of dark and yellowish browns. 



Measurements. Skull: Front of premaxillary to end of occipital 

 crest, 440; gnathion to occipital condyles, 392; gnathion to basion, 

 377; Hensel, 370; zygomatic breadth, 277; occipito-sphenoid length, 



