306 MICROTUS. 
15.5; interorbital constriction, 4.5; length of nasals, 7; palatal length, 
13; length of upper tooth row, 7. 
D. Herpetomys. 
Third upper molar with two external and one internal closed 
triangles and posterior crescentic loop, forming two internal salient 
angles; first lower molar with one external and two internal closed 
triangles, and two open triangles; third lower molar with one external 
and one internal closed triangle, and one anterior and one posterior 
obliquely transverse internal loop; plantar tubercles, 5; mamme, 6, 
4 pectoral, 2 inguinal. 
307. guatemalensis (Microtus), Merr., Proc. Biol. Soc. Wash., xu, 
1898, p. 108. 
GUATEMALAN MEADOW VOLE. 
Type locality. Todos Santos, State of Huehuetenango, Guate- 
mala. Altitude, 10,000 feet. 
Geogr. Distr. Guatemala, Central America. 
Genl. Char. Size medium; color dark; tail short, with few hairs; 
ears nearly hidden in fur. Skull: bulle large, swollen; incisive 
foramina rectangular, truncate anteriorly and posteriorly; root of 
zygoma anteriorly notched; jugals nearly parallel. 
Color. Upper parts mixed black and golden fulvous; under 
parts slaty black; lips white; tail blackish, unicolor. 
Measurements. Total length, 155; tail vertebre, 40; hind foot, 
21. Skull: occipito-nasal length, 26.5; Hensel, 23.5; zygomatic 
width, 15; interorbital constriction, 4.5; length of nasals, 7.5; palatal 
length, 13.5; length of upper molar series, 7. 
The next genus FIBER contains the Muskrats, the species most 
familiar to man probably of all the Muride, save those of the genus 
Mus, which includes those species commonly called “‘house rats and 
mice.’’ The habits of the Muskrat resemble in a considerable degree 
those of the Beaver, and their large-domed houses, formed of sticks, 
roots, and grasses are often seen rising from the surface of a pond or 
lake. The general plan of these structures is very similar to a 
beaver’s dwelling, and the entrance is beneath the water, with the 
nest or sleeping apartment toward the roof so as to be, if possible, 
above any sudden rise of the water. Holes in the banks by the side 
of streams are often made, in which the Muskrat lives, and these 
excavations sometimes cause the banks to cave in and a large portion 
of ground to disappear beneath the stream. Muskrats are shy and 
