10 
U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY-GENERAL REPORT. 
being abruptly smaller, in fact quite rudimentary. There is, however, a curious feature dis¬ 
cernible in all the species of these first two genera from the Pacific region, namely: that the 
third premolar is smaller than the fourth, instead of being larger, or at least of equal size, as 
is the case in all the specimens examined from the country east of the Rocky mountains. 
The greater elongation of the upper jaw is accompanied by a corresponding increase in the 
size of the lower, the number of teeth remaining the same. The lower incisor is pushed further 
forwards, so that its posterior extremity falls under the first premolar and half of the second, or 
at most only under the two premolars, while in Blarina the incisor is larger, stouter, and ex¬ 
tends back to beneath the middle of the first molar. 
The genus Blarina embraces the largest of the American species, one of them not inaptly 
termed talpoides. It may possibly bear division into two sub-genera of unequal number of 
premolars. Nothing analogous to this genus has been.found in the Old World. 
The following synopsis of the North American species described in this report may serve to 
render more intelligible the various subdivisions of the Soricinae. 
SORICINAE. 
Neosorex ... navigator. 
S0REX. 
A. Upper premolars five ; teeth 32. 
1. Third premolar smaller than the fourth and second. trowbridgii. 
vagrans. 
suckleyi. 
2. Third premolar larger than the fourth, smaller than or equal to the second. 
a. Premolars not imbricated ; points directed downwards. .pachyurus. 
b. Premolars imbricated. .forsteri. 
richardsonii. 
platyrhinus. 
3. Third and fourth premolars equal, and abruptly smaller than the first and second. 
cooperi. 
Tiaydeni. 
personatus. 
B. Upper premolars four ; teeth 30... Tioyi. 
Blarina. 
A. Upper premolars five ; teeth 32. talpoides. 
brevicaudus. 
carolinensis. 
B. Upper premolars four ; teeth 30, 
.cinereus. 
exilipes. 
berlandieri. 
