430 U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
This genus is distinguished from Dipus, among other characters, by having five toes on the 
hind feet, (each with separate metatarsus?) instead of but three articulated to a single. 
consolidated metatarsal bone. The tail in Dipus is densely hairy. The upper molars of Dipus 
are three instead of four. In Scirtetes the upper incisors are not grooved, and there are two 
or three metatarsal bones instead of five. 
JACULUS HUDSONIUS. 
Jumping Mouse. 
Dipus hudsonius, Zimmermann, Geographische Geschichte, I, 1780, 358, (based on Pennant’s long-legged mouse 
of Hudson’s Bay.) 
Boppaert, Elenchus Animalium, IT, 1784, 115, (from Zimm.) 
Fiscuer, Synopsis, 1829, 340. 
Meriones hudsonius, Aup. & Bacu. N. Am. Quad. I, 1851, 251; pl. Ixxxv. 
Mus longipes, (‘‘ Paut.’’) ZrmerMANN, Pennant’s Arktische Zoologie, I, 1787, 131. 
Dipus canadensis, Davies, Linn. Trans. TV, 1798, 155. 
Suaw, Gen. Zool. Mamm. II, 1801, 192; pl. clxi. 
Gerbillus canadensis, DesM. Mamm. II, 1822, 321. 
Hartan, F. Amer. 1825, 155. 
Grurrita, Cuy. V, 1827, 240. 
Gopman, Am. N. H. I, 94. 
Dipus americanus, Barton, Am. Phil. Trans. IV, 1799, 115; plate.—Is. VI, 1809, 143. 
Jaculus americanus, WAGER, Syst. der Amphibien, 1830, 23. 
 Meriones americanus, Dexay, N. Y. Zool. I, 1842, 70; plate xxiv, fig. 2. 
Mus labradorius, Jos. Sastne, Zool. App. to Franklin’s Narrative, 1823, 661. 
Gerbillus labradorius, HARLAN, F. Am. 1825, 157. 
Gopman, Am. N. H. II, 97. 
Meriones labradorius, Ricuarpson, F. B. Am. I, 1829, 144; pl. vii. 
Waener, in Schreb. Saug. IV; pl. ccexxvi, B, (from Rich.) 
Dawson, Ed. New Phil. Jour. N. 8. III, 1856, 2. 
Jaculus labradorius, WAGNER, Suppl. Schreb. III, 1843, 294. 
Kennicorr, Mammals Illinois, Pat. Office Rep. Agricultural, for 1856, (1857), 95; pl. xi. 
Meriones microcephalus, Hartan, Pr. Zool. Soc. London, VII, 1839, 1, (Philadelphia.) 
Meriones acadicus, Dawson, Ed. New Phil. Jour. N. §. ITI, 1856, 2; plate i. 
Labrador rat, Pexnant, Hist. Quad. 1781, No. 295.—Is. Arctic Zoology, I, 1782, 132. _ 
Sp. Cu.—Above, light yellowish brown; lined finely with black; entire sides yellowish rusty, sharply defined against 
the colors of the back and belly. Beneath, pure white; feet and under surface of tail, whitish. Body measuring 2.75 to 
3.50 inches; tail, 4.50 to 6.00 inches; hind feet, 1. 10 to 1. 30 inches. 
The head of this species is quite small in proportion to the body, which is thickest behind, in 
correspondence with the great development of the muscles of the hind legs. There is a very 
appreciable diminution in size from the rump to the head, without any constriction at the neck. 
The fur is coarse and stiff, owing to the development of bristly hairs among the softer fur; it 
is rather long and pressed flat to the body. The naked mufile is entirely on the under surface 
of the snout, the hairs extending around the very tip of the nose to the anterior surface, 
where it is separated sharply from the naked portion by a furrow. It appears as if the hairy 
skin could be drawn downwards so as completely to cover the nostrils. The nostrils are lateral, 
and separated by a very wide septum, indented by two furrows. The upper lip is scarcely cleft 
as far as the base of the incisors, and the space between the notch and the nose is hairy entirely. 
