646 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



d. Subgenus Microsorex, Baird, MS., 1861. 



Chars subg. — Teeth 30 (if). Upper unicuspids 4 ; the fourth mi- 

 nute, concealed from view externally by the contact of the third anicuspid 

 and first molariform tooth ; the third appreciably smaller than the second 

 and first, which are equal to each other and to the hook of the incisor. 

 Interior snag and posterior hook of upper incisor well developed ; lower 

 incisor with (normally) two denticulations, and extending so far back 

 that the two succeeding teeth are placed entirely above it. Teeth all 

 "well colored. Coronoid process of jaw long and comparatively slender. 

 Molariform teeth large ; distance between their outer edges more than 

 half the width of the skull. Depth of rostrum (including jaw) greater 

 than that of the cerebral portion of the cranium. Series of molariform 

 teeth longer than half the length of the whole series of teeth. External 

 characters not obviously different from those of Sorex proper. Tail 

 about as long as trunk. 



Type. — Sorex hoyi Baird, from which S. thompsoni does not appear to 

 be specifically distinguishable. 



This perfectly valid section of iSorex has been suspected to rest upon 

 immature dentition, the decrease in the number of teeth being supposed 

 due to suppression or non-development of the minute last uuicuspid. 

 But it will be seen from the foregoing that this minute tooth, immedi- 

 ately preceding the first molariform tooth, is present in both cases, being 

 in Sorex proper preceded by four larger unicuspids, while in Microsorex 

 the unicuspids preceding it are only three in number. 



e. Subgenus Notiosorex, Baird, MS., 1861. 



Chars, subg. — Teeth 28 (if) ; upper unicuspids 3, the minute last uui- 

 cuspid of Sorex proper and Microsorex here wanting ; first and second 

 unicuspids about equal to each other, larger than either the third 

 unicuspid or the posterior hook of the incisor. N"o internal snag or 

 notch on upper incisor, and the posterior hook only moderately devel- 

 oped, being smaller than the succeeding tooth. Lower incisor with only 

 one denticulation, or merely a slight sinuation ; its tip hooked upward, 

 its base reaching below the two succeeding teeth. Teeth scarcely colored, 

 and only on the tips of the incisors and a few succeeding teeth, the 

 molariform ones left white. Coronoid process of jaw comparatively 

 short, obtuse, and widely diverging outward. Proportion of molariform 

 teeth to the rest of the series" and width across them relative to the 

 cranial width as in Microsorex. Skull very low behind, broad across 

 the orbits, and comparatively little attenuate in front. Bars remark- 

 ably large, thinly haired, and conspicuous. Tail short, somewhat as in 

 Blarina, scarcely or not half as long as the head and body. General 

 external appearance of Grocidura. 



Type. — Sorex {Notiosorex) crawfordi^'AuA^ MS., 1831, sp. n., described 

 at lensfth beyond. 



