320 MAMMALIA: GLIRES. XLVIII. 



/. Mouse-like; length with tail 4 to 8 inches. 



g. Upper incisors grooved ......... OCHETODON, 546. 



gg. Upper incisors not grooved; ears very large. . CALOMYS, 547. 

 ff. Rat-like; length, with tail, a foot or more. . . . NEOTOMA, 548. 



ee. [Molars of upper jaw with tubercles in three series; soles naked; tail 

 long, scant-haired or scaly. (Introduced species).] .... Mus. 



542. FIBER Cuvier. (Lat., beaver.) 



1039. F. zibethicus (L.). MUSKRAT. Color dark brown. L. 

 22^. T. 11. N. Am. ; everywhere. Largest of our Muridce ; build- 

 ing houses or burrows about streams and ponds. (Lat., zibetha, the 

 Civet, from the odor.) 



543. S YNAPTOMYS Baird. (awaiTTa, to join ; p.vs, mouse.) 



1040. S. cooperi Baird. LEMMING MOUSE. Mouse-color, gray- 

 ish below ; head very large with long whiskers ; fur soft and long. 

 L. 4|. T. f . Indiana (Brookville, Nashville) to Oregon and 

 Alaska, a remarkable animal, between the field-mice and the lem- 

 mings (Myodes). (To Dr. J. G. Cooper.) 



544. ARVICOLA Lacepede. FIELD MICE. (Lat., arvum, 



field; Colo, I inhabit.) 



a. Posterior upper molar with one exterior triangle and a posterior trefoil; 

 middle upper molar with one internal triangle ; front lower molar with 

 two internal and one external triangle. 



b. Fore claws larger than hinder; fur dense, silky, mole-like; size small. 

 (Pitymys McMurtrie.) 



1041. A. pinetorum Le Conte. PINE MOUSE. Chestnut color, 

 ashy below. L. 4f . T. f 1ST. Y. to 111. and S. (Lat., of the 

 pines.) 



bb. Fore claws not larger than hinder; fur coarse, not glossy; size medium. 

 (Pedomys Baird.) 



1042. A. austerus Le Conte. Grizzly brownish, rusty plumbe- 

 ous below. L. 5^. T. 1. Mich, to Dak. and La. (Lat., harsh.) 

 aa. Posterior upper molar with two external triangles and a posterior cres- 



cent; middle upper molar with two internal triangles; front lower 

 molar with three internal and two or three lateral triangles; size large. 

 (Mynomes Rafinesque.) 



1043. A. pennsylvanicus Ord. MEADOW MOUSE. Fore 

 claws not longer than hind claws. Grayish brown, blackish 

 mesially, hoary below. L. 5^. T. Ij. U. S., generally abun- 

 dant ; variable. ( A . riparius Ord, a later name.) 



545. EVOTOMYS Coues. (*, well ; ovs, ear; pvs, mouse.) 



1044. E. rutilus (Pallas). LONG-EARED MOUSE. Color chest- 

 nut, median line of back rusty-red; sides yellowish, belly dull 

 white; fur full and soft; ears prominent. L. 4^. T. 1|-. North- 



