930 MONOGRAPHS OF NORTB AMERICAN RODENTIA. 



Nebraska, Wyoming, Utah, Colorado, and New Mexico, as well as from bone 

 ca\cs and Quaternary deposits of the East,. Within the last six years, 

 more than fifty species have been named, but very few of them can be 

 said to have Keen characterized, owing to the imperfect nature of the mate- 

 rials from which they have been made known. In 1873, Dr. Leidy described 

 and figured remains of six species in his great work entitled "Contributions 

 to I he Extincl Vertebrate Fauna of the Western Territories",* of which four 

 were referred to the Sciuridce and two doubtfully to the Muridce. Professor 

 Marsh, in 1871 and 1872, gave preliminary descriptions, without figures, of 

 ten or twelve species, in the American Journal of Science and Arts (vols, ii 

 and iv, ;')d series), of which a large part are doubtless referable to the Sciuridce, 

 but in many instances no conjecture is offered respecting their affinities. In 

 nearly every case, the species were described from one or two imperfect jaw 

 fragments, containing one or more molar teeth, but in one or two instances 

 merely from isolated molars. Professor Cope, in various papers, has described 

 a still larger number, making altogether about fifty-four species, and six- 

 teen genera, all more or less imperfectly indicated. In many cases, owing 

 to the fragmentary and extremely unsatisfactory nature of the remains on 

 which the diagnoses have necessarily been based, the affinities of many of 

 the genera can scarcely be even conjectured. Some are positively referable 

 to the Muridce, others to the Casloridce, Leporidce, and Hystricidce, while many 

 others are unquestionably referable to the Sciuridce. Other remains belong 

 to families unrepresented in the existing fauna, as the Ischyromyidie and 

 ( 'asloroididce. 



Remains of Glires have been found in great variety in the Tertiary (Eocene) 

 deposits of the Upper Green River and its tributaries, and in portions of Col- 

 orado, Dakota, and Nebraska. Other remains, in part referable to species 

 still existing, but mainly to extinct species of existing genera, have been found 

 in the caves of Pennsylvania and Virginia, and in the crevices of the lead- 

 bearing rocks of Illinois and Wisconsin in deposits of Quaternary age. In 

 a few instances, as in the case of Palcwlagus in Colorado, large numbers of 

 specimens of the same species have been found, but generally the species are 

 known as yet from merely a few imperfect fragments of jaws. 



In respect to the Sciuridce, the bone-caverns of Pennsylvania and Vir- 

 ginia have afforded remains of extinct species of Tamias and Sciurus, but, 



• final Reports of tlie U. S. Geol, Surv. Terr. vol. i, Fossil Vertebrates, part i, 1873. 



