COUES ON INSECTIVOROUS MAMMALS. 637 



teeth are colored, and these but slightJ.v. In all the rest, the teeth 

 are heavily pointed with color, as in Sorex vulgaris of Europe, with 

 which our Sorices of 32 teeth are strictly congeneric. This color is 

 usuall}' described as "chestnut"; it varies much in intensity, from piceoiis 

 reddish-black, through rich burnt sienna, to quite light and bright red. 

 The younger teeth appear to be the more heavily colored ; they take 

 color with their early development. Since, too, it is their points that 

 are most heavily colored, wearing of the dentition gradually lightens 

 the tint at the same time that it decreases its extent. 



The Shrews are remarkably voracious auimals, like the Moles, requir- 

 ing a large supply of food, and the ceaseless working of their jaws 

 results in attrition of the teeth to such degree that the appearance is 

 greatly altered with age. In extreme cases, the cusps of the molars, 

 ordinarily so conspicuous, are entirely ground away, the premolars are 

 reduced to mere stumps, while the fangs of the upper incisors and the 

 curious denticulations of the lower incisors suffer quite as much. Teeth 

 of the same or very closely allied species vary remarkably in their 

 appearance as a whole, probably according to age ; the variation being 

 (besides the actual shortening of the teeth) in the apparent set or "dip " 

 of the anterior teeth, the degree to which they are " tiled " or imbricated 

 at base, and in the obliquity with which the anterior incisors connive. 

 The precise nature and purport of these observed differences in the same 

 or closely allied species, and the reliability of certain assumed specific 

 characters thereby afforded, remain matters for further investigation. 



I may here allude, however, to the curious fact first pointed out by 

 Professor Baird, and which I have verified, of the modification of the 

 premolar dentition which the Western species collectively, as compared 

 "with the Eastern, have undergone. A striking peculiarity of all the 

 Western species, no matter how diverse in other respects, is to have the 

 "third premolar" decidedly smaller than the "fourth"; while, in all the 

 species east of the Eocky Mountains (with one possible exception), 

 the same tooth is as large as or larger than the other. Of the fact there 

 is no question ; it may be observed in an instaut, and is unmistakable. 

 Its significance is another thing. Some of the Western species are 

 scarcely distinguishable. If at all, from their respective Eastern ana- 

 logues, except by this character, and they all show it. It is even re- 

 peated in Neosorex navigator, as compared with i^. paUistris. What 

 relation tiiis condition bears to the Pacific fauna it is difficult to under- 

 stand. We may practically recognize it in two ways : by giving it 

 prominence as a leading feature, by which two groups of Sorex proper 

 may be discriminated, or by reducing it to merely a secondary charac- 

 ter of certain species, irrespective of geographical distribution. To pur- 

 sue the former course would be to rather widely separate certain species 

 hardly or not distinguishable except by this technical character; to 

 adopt the latter alternative would be to ignore a generalization equally 

 legitimate and curious, that may have important if unsuspected rela- 



