158 [SEPTEMBER 
Much of the confusion in the species has arisen from a laudable desire to iden- 
tify and retain the names of the older authors, even when unsupported by suffi- 
cient descriptions. Science has now, however, advanced so far, that it is time to 
get rid of all hypothetical synonyms, by excluding definitely all that is too im- 
perfect for use, even when sanctioned by great age or character. I have accord- 
ingly placed at the end of this paper, references to all such descriptions as seem 
to be unfit for quotation under any individual species, and would recommend that 
these having now been collected together, should be hereafter passed over in re- 
spectful silence. 
The synonyms of this genus.are as follows:—Gromys Raf. (1817); 
[DirLtostoma Raf. (1817) ;] Saccorpuorus Kuhl. (1820); Ascomys Lichtenstein, 
(1822); Psruposroma Say, (1823); Orycromys Eydoux, (1837); THomomys 
Wied. (1839). 
The two last names belong only to the second division of the genus, or those 
with smooth incisors, that character having been assumed as of generic value. 
The following analytical table expresses the relation between all the species 
which I have had an opportunity of examining. Four species of Richardson be- 
longing to group B. and G. castanops, the place of which is uscertain, have not 
been included, as [ have not seen them, and can only take what has been written 
by others upon them. 
A. Dentes primores superiores profunde sulcati. 
a. Cauda fere nuda. 
1. Rufo-fuscus fere hispidus 
2. Supra rufus : primores superiores bicaniculati 
3. Supra plumbeus: primores superiores unisulcati 
. hispidus Lec. 
. canadensis Lec. 
- pineti Raf. 
RAD 
b. Cauda pilosa. 
4. Supra nigricans, primores superiores unisulcati G. mexicanus Rich. 
5. Supra fuscescens, primores superiores bicanaliculati ©G. oregonensis Lec. 
B. Dentes primores non sulcati. 
6. Supra rufescens, infra albicans, auribus brevibus G. rufescens Lec. 
A. Dentibus primoribus sulco profundo exaratis. 
a. Cauda fere nuda. 
1. G. hispidus, pilis concoloribus rufo-fuscis minus subtilibus tectus, cauda 
brevi nuda, auribus obsoletis. 
Length from nose to root of tail, sa) : a 11-5 
Tail, A 5 : j 5 “ 3. 
Anterior foot to end of claw of third toe, : 4 1°7 
Posterior foot to end of claw of third toe, ‘ 4 1:9 
One specimen, Mexico, Mr. Pease’s collection. This species differs from all 
the others in having the fur very coarse and harsh, and entirely of a reddish 
brown color. . Beneath it is slightly grayish, but the difference in color is by no 
means obvious. ‘The ears are not at all prominent, being merely openings in the 
skin. ‘The whiskers are as long as the head. The upper incisors are broken off, 
but enough remains to show that they were deeply grooved near the middle of the 
anterior surface; it is impossible to determine if there is a second submarginal 
groove. ‘The tail is completely naked except at the root. The feet are precisely 
as in the other species of this division of the genus. 
2. G.canadensis, supra rufus, infra flavicans, pilis subtilibus, basi saturate 
plumbeis, genis pedibusque albidis, cauda mediocri nuda, auribus_ brevibus, pri- 
moribus superioribus bisulcatis. 
Length from nose to root of tail, . 5 : % 6°7 
CC eat : : ‘ % , : 3°2 
Anterior foot to end of third elaw,  - ‘ : 5 1:3 
Posterior foot to end of third claw, ; ; i 13 
