644 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



American species, and it is the only Old World type found in this 

 country, Crossopus being replaced by Neosorex, and Crocidura having no 

 exact analogue, though the new subgenus Notiosorex may be considered 

 to answer to it. 



Among our numerous species of Sorex, however, is found considera- 

 ble diversity of external characters, coupled with difference in the nu- 

 merical composition of the teeth, enabling us to mark oft three sections 

 with ease. The teeth are either 28, or 30, or 32, according to the num- 

 ber of upper unicuspids, whether 3, or 4, or 5. Other distinctions may 

 be drawn from the relative proportions of the unicuspids and from cer- 

 tain conditions of the tail, feet, and ears. 



The species of American Sorea? at large offer the following characters: — 



Body slender, head elongate, and muzzle attenuate; breadth of the 

 head nearly or about half its length ; muffle naked, with a terminal 

 vertical furrow continuous with the horizontal one formed below by 

 meeting of the lips, i. e., end of the snout bilobate; nostrils lateral j 

 whiskers long, some of them reaching beyond the head; ears large 

 (comparatively), with auricle directed backward (as usual) ; the aute- 

 tragus elliptical or semicircular, fitting and closely applied to the meatus, 

 its upper root passing beneath a second transverse nearly horizontal 

 flap, which projects forward and forms a second valve, closing the 

 remaining portion of the naked auditory region. Both faces of these 

 flaps are generally naked, the anterior always so ; both surfaces of the 

 auricle are thinly haired, while its edge and the edges of both the flaps 

 are fringed with long hairs. The fore feet are from one-half to two- 

 thirds as long as the hinder ones ; both are naked below ; the sides of 

 the heels, however, are hairy, leaving only a narrow strip bare. The 

 soles are paved with small granulations, among which are six large 

 tubercles, one at the base of respectively the first, second, and fifth 

 digits, one common to the bases of the third and fourth, and another 

 on each side of the sole midway between the heel and the bases of the 

 digits. The feet are not fimbriate in the sense that those of Crossopus and 

 JSIeosorex are. The tail is generally subequal to the trunk alone, sooae- 

 times, however, about as long as the head and body ; in only one 

 instance known to be less than half this latter dimension. It is more 

 or less thickly, but uniformly, covered with hairs, which usually form a 

 slight pencil at the tip ; but under some conditions, probably seasonal 

 or otherwise fortuitous, the tail is neaxly naked. 



The skull is slender, constricted behind the molars. The upper 

 unicuspids are 3, 4, or 5. When 3, they are regularly graduated in 

 size, none being very small. When 4, the first three are graduated 

 in size, the fourth being abruptly smaller and very minute, scarcely 

 visible from the outside, and liable to be overlooked, so crowded is it 

 between the closely approximated or even touching teeth which 

 precede and follow it. When 5, the first four are abruptly larger 



