MAMMALIA. 199 
naturalists; and the American systematic writers have either overlooked M. 
Rafinesque’s species entirely, or referred them all to the mus bursarius. In the 
latter case, they are undoubtedly wrong, for there are at least six or seven distinct 
species belonging to one or other of these genera, which inhabit America ; and I 
think that both geomys and diplostoma will eventually prove to be good genera: — 
the Sand-rats belonging to the former having cheek-pouches, which are filled from 
within the mouth, and the gavffres or camas-rats of the latter genus having their 
cheek-pouches exterior to the mouth, and entirely unconnected with its cavity. 
I have had no opportunity of examining the geomys pinetis, which is the type of 
the genus; but Mr. Leadbetter, with his wonted liberality, has permitted me to 
inspect an individual of a hitherto undescribed species from Cadadaguios ; and 
Mr. David Douglas very kindly sent me a specimen of another species, which he 
captured on the banks of the Columbia, and which forms the subject of the 
following article. From these two the characters of the genus, given in the preced- 
ing pages, were drawn up, the description of the teeth, and the views of the scull, 
being made from the latter. With regard to the Canada pouched-rat, great doubt 
still exists as to whether it belongs properly to geomys or to diplostoma. It was 
first described by Dr. Shaw, and an engraving published in the Linnean Trans- 
actions, from a drawing by Major Davies, of a specimen sent to Governor Prescot, 
from the interior of Canada. Judging merely from that figure and description, I 
should have little doubt of the cheek-pouches opening into the mouth, and of their 
being precisely similar in form and functions to the cheek-pouches of the sand-rats ; 
but I have been told, on good authority, that the identical specimen described by 
Shaw (and which, en the dispersion of Mr. Bullock’s collection, passed into the 
hands of M. Temminck) is, in fact, similar to the gauffres, in having cheek-pouches 
that open exteriorly, and that consequently Major Davies’s drawing represented 
them in an unnatural, inverted position. Mr. Say, under the generic name of 
pseudostoma, gives the characters of a Missouri gauffre, with cheek-pouches 
opening exteriorly, and he identifies his specimen with the mus bursarius. He 
alludes to the Georgia hamster, as belonging to the same genus, without giving 
any further account of its characters than merely quoting Dr. Barton’s remark, of 
its being only half the size of the Missourione. His account of the dentition of the 
Missouri gauffre corresponds, as far as it goes, pretty closely with that of the 
Columbia geomys. Dr. Harlan and Dr. Godman refer the Georgia, Canada, and 
Missouri animals, to one species. 
