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U. S. P. R. R. EXP. AND SURVEYS—-ZOOLOGY—GENERAL REPORT. 
Tribe II. Arctomyina. —The first upper molar equal in length to the second, and about one- 
half or one-third the size ; swollen at the base ; conico-acuminate at the apex, truncate at the 
point, compressed and more or less lobed, more rarely simple but always with a slight pit 
behind. The crowns of the larger molars, except the last, are trigonal, wedge-shaped, with 
two shorter ridges formed by the anterior and posterior edges of the tooth itself, and two inter¬ 
mediate larger ones, generally quite elevated and acute. The anterior dentiform tubercles of 
the lower molars exceed almost twice the height of the bases of the crowns. The ridges of the 
soft palate between the molars almost double the molars in number and considerably approxi¬ 
mated. The third finger always longer than the rest. Claws considerably elongated, trigonal, 
and dilated at the base ; moderately curved. 
