636 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



and Gophers, and which my friend Mr. Allen has admirably brought out 

 in his studies of the Squirrels. In some cases, I find almost identical 

 effects of climatic or other conditions upon the Shrews and the Mice of 

 particular localities, by which they both acquire the same fades loci. 



Present indications are that the normal variability of the Shrews in 

 size, shape, and color is not less than has been determined to hold good 

 in various other families of Mammals. But our species have yet to be 

 handled with full appreciation of this fact, and revised accordingly. 



Besides these general conditions of variability, there are some pecu- 

 liar to Tnsectivora. The tail and lips, if not also the feet, are known to un- 

 dergo extraordinary changes in connection with the rutting season. 

 The remarkable swelling of the tail of the shrew-like Mole, Gondylura 

 cristata, finds its representation, if in less degree, among the Shrews, 

 associated with tumidity of other parts. These facts are known at large, 

 yet their practical application in the discrimination of species has been 

 too limited. The implication of all such terms as ".pachyurus ", " longi- 

 rostris", " platyrhinus ", must be cautiously accepted. 



The skull and teeth offer a ready means of throwing our species into 

 genera and lesser groups, and no step in the study of the Shrews can 

 be safely taken without examination of the cranial and dental characters. 

 The skulls which come into our hands are very commouly mutilated or 

 defective as to the back part, such is the fragility of the cerebral por- 

 tions; but fortunately the rostral portion, including the jaw, is unusually 

 strong for its size, and, with the teeth, is generally available for study. The 

 dental armature of the Shrews is singularly powerful, far surpassing, in 

 relative strength, that of the large Carnivores. 



IsTotwithstauding assertions of authors to the contrary, the number of 

 the teeth of the Shrews is constant in the same species. Replacement 

 of the temporary teeth is said to occur in the foetus ; at any rate, speci- 

 mens occur so young that the teeth are still encapsuled in membrane, 

 which, nevertheless, show the normal adult number and permanent rel- 

 ative position when this envelope is torn off. All the American Shrews 

 hitherto known have either 32, 30, or 28 teeth. The number in the lower 

 jaw is the same for all, namely, 12. The difference in the upper jaw oc- 

 curs in the "lateral" teeth intermediate between the large anterior inci- 

 sor and the first molariform tooth. It has been wrongly supposed by 

 at least one author that the Blarince and Sorices of 30 teeth were respect- 

 ively the young of those of 32 teeth. In the case of the 30-toothed 

 Sorex, the validity of the numerical distinction is curiously proven by 

 the fact that it is not the minute tooth immediately precediug the large 

 molariform premolar which is wanting, but one of the preceding pre- 

 molars. The minute tooth is there still, but it is preceded by only 3 in- 

 stead of 4 lateral teeth. In the new subgenus proposed beyond, iu 

 which there are but 28 teeth, it is the same premolar which is wanting. 



We have no known white-toothed Shrews in America, like Crocidicra 

 aranea, though in our 28-toothed species the points of only a few anterior 



