282 EXPLORATION OF THE CANONS OF THE COLORADO. 
ance; if the vertebrae be left in, it shrinks tightly around them in drying, 
displaying not only the joints, but also the shape of the individual bones. The 
hind feet share this nakedness, but not to the same extent ; the instep is 
nearly bare, but the toes are sparsely pilous with short colorless bristles. The 
back of the fore feet is in much the same condition. The depilation of the 
members is not always as complete as here described ; but such is the unmis 
takable tendency in all cases, and such the accomplished result in the majority 
of examples in adult life. Younger specimens, in the plumbago state of 
pelage, show as hairy tail and feet as an average sample of G. bursarius, and 
before the incisors have attained maturity, so as to afford fair characters, 
might readily be supposed to be G. bursarius, were locality not taken into 
account. Of such character is No. 1500, Museum of the Smithsonian Insti 
tution, particularly mentioned by Baird, op. cit., p. 382. 
My material is abundant for a table of measurements of this species ; 
but it seems unnecessary to prepare one, since it would be simply an amplifi 
cation of the statement that the animal does not differ at all from G. bursarius 
in size or shape. For the same reason, it is unnecessary to enter into 
further description after presenting the two characters (particular style of 
sulcation of incisors and nakedness of tail and feet) in which solely does the 
species stand apart from G. bursarius. 
Under these circumstances, it might be held by some that the present is 
merely a localized race of G. bursarius ; and I should be the last one to dis 
pute such statement of an abstract fact. This Geomys is, of course, an off 
shoot of the bursarius stock ; and, for that matter, so are all the rest of the 
"species" modified descendants of some one stock. It would be only shifting 
the question a peg to require that the fact should affect the nomenclature. A 
"permanent variety" is a contradiction in terms. This is the case: Here is 
a set of individuals differing thus-and-thus (as above described) from another 
set. The difference is slight, but constant; there is no intergradation, for 
the simple reason that the two sets of animals now occupy different geograph 
ical areas, are completely isolated from each other, and thus cut off from 
interbreeding ; or, in other words, from reproducing offspring in which the 
characters of both parents are blended. It is quite possible that, in their 
blind movements under the ground, the two may come together and interbreed ; 
