156 GLIRES. 
A. Myonomes, Coues (ex Rafinesque), Proc. Ac. Philad. 1874, p. 189. “Back 
upper molars with fwo external triangles and a posterior crescent; middle 
upper molar with ¢wo inner triangles; front lower molar with three internal 
and two or three external lateral triangles” (Cowes). Claws of fore feet not 
larger than those of hind feet ; soles of latter with six tubercles. 
1. A. mexicanus. Upper parts dark brown, washed on the sides with rufons ; lower 
parts grey, tinged on the breast with yellow; feet dusky. Ears moderate, 
hairy, with a well-developed antitragus. Tail hairy, indistinctly bicolorous, 
somewhat longer than the hind foot. Length of head and body about 4-25, 
of tail 1-00 to 1-15, of hind foot 0:72. 
B. Pirymys, M*Murtrie, Amer. ed. of Cuvier’s Régn. An. i. p. 434 (1831, fide Baird). 
“ Back upper molar with one external angle and a posterior trefoil; middle 
upper molar with ove internal angle; front lower molar with ¢wo internal and one 
external triangle” (Cowes). Claws of fore feet longer than those of hind feet ; 
soles of latter with five tubercles; fur fine, glossy. 
2. A. pinetorum. Upper parts brown, more or less tinged with rufous; lower 
parts silvery grey; tail shorter than the head, but distinctly longer than the 
hind foot. Length of head and body about 3°60, of tail 0-70, of hind foot 0'"63. 
3. A. quasiater. Upper parts almost black, shaded with dark chestnut, and 
passing into the blackish ash of the lower parts. Tail little longer than the 
hind foot. Length of head and body about 4’-33, of tail 0-70, of hind foot 
0-66. 
It may here be observed that the Musquash or Musk-Rat, Fiber zibethicus (Schreber), 
is found in New Mexico and Arizona; but we have no evidence of its existence within 
our present limits. 
1. Arvicola mexicanus. 
Arvicola (Hemiotomys) mexicanus, de Saussure, Rev. et Mag. Zool. 1861, p. 3 (descr. orig.)’. 
Hab. Muxico (de Saussure'), San Juan (Rébouch, Mus. Brit.), Tehuantepec (Boucard, 
Mus. Brit.). 
It is with great hesitation that I provisionally retain this Vole as specifically distinct 
from the well-known Arvicola riparius, Ord, of North America. M. de Saussure’s short 
diagnosis, quoted below*, is all that has yet been published on the subject, so far as I 
am aware ; and it appears to have escaped the keen research of Dr. Elliott Coues. Mr. 
* “Medius, supra fuscus, subtus cinerascens, pilis cinereis, apice fuscis. Auricule sat magne, fimbriatee, 
antitrago magno. Vibrissz capite breviores, fusce. Pedes antici paulo longiores posteriorum dimidio ; postici 
elongati, subtus basi pilosi, tuberculis 6 instructi, quorum posticus magnus, penultimus minutus [sic]. Ungues 
anteriores posterioribus haud majores. Cauda brevissima, pedibus posticis paulo longior at capite brevior. Cor- 
poris longitudo 0°110; caudee 0-019 ; pedis postici 0-016.” 
