748 
EXPLANATION OF THE PLATES. 
Page. 
Fig. 3— Hesperomys hoylii, Baird.—No. 1270.—Middle fork of American river, Cal.... 471 
Keferences (i-g, as in fig. 1; /and g magnified nearly three diameters. 
Fig. 4— Hesperomys {Ory^omys) palustris. — 6—No. 2111.—Society Hall, S. C. 482 
Keferences a-g, as in fig. 1. 
Fig. 5— Hesperomys texanus, Woodh.—No. 2217.—Turkey creek, Texas. 464 
Grinding surfaces only of the molar teeth ; a —of left upper molars ; h —of 
left lower molars, magnified rather more than twice. 
Fig. 6— Mus tectorum, Savi.—White-hellied rat.—No. 1685.—Cadcreita, New Leon.... 441 
Keferences a-g, as in fig. 1; / and g magnified twice. 
PLATE LIII. 
Fig. 1— Neotomafuscipes, Cooper.—Bush rat.—No. 2040.—Santa Clara, California.... 496 
Male quite old. a —skull from below ; 5—skull from above; c—skull from 
the side ; d —left side of lower jaw ; e —left side of lower jaw from above; 
/—upper molars of left side ; g —lower molars of left side. The two last 
magnified three times. 
Fig. 2— Neotoma jioridana, Say & Ord.—Wood rat.—No. 2056.—St. Simon’s island, 
Georgia. . 487 
Very large and old. Keferences a-g, as in the last. Two last magnified 
three times. 
Fig. 3— Neotoma occidentalis, Cooper.—Brush-tailed rat.—No. 1591.—Shoalwater bay. 
Washington Territory. 496 
Not very old. Keferences a-g as in fig. 1 ; / and g magnified twice. 
Fig. 4— Neotoma magister, Baird.—Fossil; from the hone cave at Carlisle, Pa. 498 
a —left side of lower jaw ; 6—left side of lower jaw from above. 
Fig. 5— Neotoma cinerea. —Kocky Mountain rat.—No. 2159.—Fort Sarpy? Yellow¬ 
stone river, Nebraska. 499 
Keferences a-g as in fig. 1 ; / and g magnified rather more than twice. 
Fig. 6— Sigmodon herlandieri, Baird.—Texas cotton rat.—No. 1672.—West of San 
Antonio. 504 
Very old. Keferences a-g as in fig. 1; / and g magnified rather more than 
three times. 
Fig. 7— Sigmodon herlandieri, Baird.—No. 1681.—Santa Kosalia, Mexico. 504 
Kather young, a —grinding surface of left upper molars ; 5—grinding 
surface of left lower molars. Magnified nearly three times. 
PLATE LIV. 
All the figures in the present plate represent the grinding surfaces of the molar teeth 
on the left side of the jaw. The one above the number belongs to the 
superior molars, the lower figure to the inferior ones. 
No. 1719— Arvicola pinetorum, Lee.—No. V^V*—Georgia. 544 
No. 1714— Arvicola cinnamomea, Bd.—No. Wr-— <? • Penibina.^. 541 
No. 2211— Neotoma mexicana, Bd. — No. Pedro river, Sonora. 490 
