GEOMYS.—THOMOMYS. 161 
and these were all killed with a blow from the machete or bush-knife an Indian always 
carries with him. The underground workings of these animals show themselves in the 
heaps of mould cast up here and there in the track, reminding one of the similar labours 
of the common Mole in Europe. But the underground passage is of considerable size, 
so as to cause much annoyance if the surface above gives way under the foot of a passer 
by. In the upper parts of the Volcan de Fuego, at an altitude of from 10,000 to 13,000 
feet, similar workings are very abundant in the loose volcanic soil: but Messrs. Godman 
and Salvin never succeeded in obtaining a specimen from there; so that it is not certain 
by what species these workings are made, though probably by this animal, so common 
at a lower elevation. 
Two specimens of this Gopher in the Berlin Museum (one labelled as being from 
Peten, the other without locality) are irregularly marked with white, which forms a 
broad but interrupted band over the loins. 
2. THOMOMYS. 
Thomomys, Max. zu Wied, Nov. Act. Acad. Cas. Leop.-Car. xix. p. 23 (1839). 
The principal external distinctions between this genus and the last have already been 
noticed in comparison; but it should be added that the striking characters afforded by 
the plain incisors, well-developed ear-conch, and moderately clawed feet of Thomomys 
are supported by a number of cranial differences, which have been worked out in great 
detail by Dr. Coues*. That zoologist has pointed out another point in which the two 
genera do not agree—namely, “that in Geomys a number of species appear to have become 
firmly established, while the differentiation of Thomomys has not progressed so far.” 
With much more material than any previous writer has enjoyed, Dr. Coues recognizes 
; only two species of Thomomys; one of which, 7. talpoides (Richardson), is divisible 
into three geographical races, inhabiting respectively the northern interior, the Pacific 
coast, and the southern interior of the North-American continent, but each intergrading 
into the other. The southern type, formerly kept separate as 7. wmbrinus (Richard- 
son), is small in size, the length of the head and body averaging about 6°50, and that 
of the tail 2-20. Its colour is very variable, presenting various shades of fawn, reddish- 
brown, brown, and greyish-brown, the lower parts being only paler than the upper. 
There are usually some blackish markings about the nose and mouth; and occasionally, 
as in the other races, the animal is jet-black all over. 
The only other Thomomys to which Dr. Coues grants specific distinction is his own 
T. clusius?, founded on a single specimen from the Rocky Mountains. This appears 
to be a much smaller animal than any of the races of 7. talpoides, and to be -distin- 
guished by its very short tail and by its lower parts and limbs being pure white. 
* Rep. Powell’s Expl. Colorado River (1875), pp. 217-285. 
+ Proc. Ac. Philad. 1875, p. 188 (descr. orig.); Mon. N.-Am. Rodent. p. 629, pl. vii. 
BIOL. CENT.-AMER., Mamm. Vol. 1, Octoder 1880. Y 
