Vol. 5] 



Kelt ogg. — Bode n t Fan na. 



425 



anterior tubercles and a heel consisting of a curved ridge, while 

 Plesiarctomys, Sciurus, Sciuroides, Pseudosciurus, and Sper- 

 mophilus all have four tubercles which tend to pair anteriorly 

 and posteriorly into transverse ridges and form a square tooth. 



This form is nearest to Arctomys primigenia, an extinct 

 species from the Pleistocene of Paris, the chief difference between 

 the two being that A. primigi ma has a distinct, separate tubercle 

 on the anterior face of P 4 , while in A. nevadensis there is a ridge 

 starting from the base of the metaconid 1 and showing only the 

 slightest indication of a separation where it joins the protoeonid. 

 Other points of difference arc in the larger size of P 4 and M,, in 

 A. nevadensis, their more nearly square form and more oblique 

 setting; the smallness of the incisor in proportion to the other 

 teeth ; and in the symphysis ending posteriorly in front of the 

 mental foramen instead of back of it as in A. primigenia. Prom 

 the living species, A. mondx, A. flaviv enter, A. dacota, and from 

 the extinct species, A. vetus, A. nevadensis differs in its greater 

 size; more particular differences being that A. monax has the 

 anterior tubercles of the teeth much lower, and A. flaviventer 

 has a low metaconid, the teeth are more nearly square and the 

 tubercles not so oblique. As compared with Palaearctomys 

 montanus, this species shows small incisors and large P 4 and M 4 , 

 and the jaw itself is larger and heavier. 



ARCTOMYS MINOR, n. sp. 

 Figs. 3, i, 5, 6, and 7. 



Type, no. 12538, Univ. Calif. Col. Vert, Palae. Left P 3 and 

 P 4 witli part of the maxilla ; right M 2 and M 3 with portion of the 

 lower jaw; right P 4 . M,, and M 2 ; and the anterior portions of 

 the upper and lower incisors. From locality no. 1083 at Thousand 

 Creek, Humboldt County, Nevada. 



Specific Characters. — P 4 has a slender metaconid not much 

 higher than the protoeonid and the two are connected by a ridge, 

 whereas in other species both tubercles are high and no1 con- 

 nected by a ridge. Protoeonid and hypoconid far apart witli 



i In this paper, the nomenclature used in descriptions of lower premolar 

 teeth is the same as that commonly followed in designation of the tubercles 

 of lower molars. 



