930 “MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
Nebraska, Wyoming, Utah, Colorado, and New Mexico, as well as from bone- 
caves and Quaternary deposits of the Kast. Within the last six years, 
more than fifty species have been named, but very few of them can be 
said to have been 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 the Extinet Vertebrate Fauna of the Western Territories”,* of which four 
were referred to the Sciuride and two doubtfully to the Muride. 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. i 
and iv, 3d series), of which a large part are doubtless referable to the Sciuride, 
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 Muride, others to the Castoridea, Leporidz, and Hystricide, while many 
others are unquestionably referable to the Sccwride. Other remains belong 
to families unrepresented in the existing fauna, as the IJschyromyide and 
Castorovdide. 
Remains of Giires 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 Palgolagus 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 Sciuride, the bone-caverns of Pennsylvania and Vir- 
gimia have afforded remains of extinct species of Tamias and Sciurus, but, 
* inal Reports of the U. 8. Geol. Surv. Terr. vol. i, Fossil Vertebrates, part i, 1873. 
