Illustrations. ix 
LIST OF ILLUSTRATIONS. 
PLATES. 
1 — Skulls of North American Squirrels. Figs. 1-3, Sciwrus vulgaris leucourus (for 
comparison); Figs. 7-9, Batosciurus deppei vivax; Figs. 10-12, Tamiasciurus 
hudsonicus gymnicus. 
I1.—Skulls of North American Squirrels. Figs. 1-3, Echinosciurus aureogaster hypo- 
pyrrhus; Figs. 4-5, E. poliopus cervicalis; Figs. 6-7, E. eee variegatoides; 
Fig. 8, LH. melania. 
Iil.— Skulls of North American Squirrels. Figs. 1-3, Neosciurus carolinensis caro- 
linensis; Figs. 4-6, Hesperosciurus griseus griseus. 
IV.— Skulls of North American Squirrels. Figs. 1-3, Otosciurus aberti aberti; Figs. 
4—6, Parasciurus arizonensis. | 
V.— Skulls of North American Squirrels. Figs. 1-2, Parasciurus niger rufiventer; 
Figs. 5-6, P. oculatus oculatus; Figs. 8-9, P. apache. 
VI.— Maxillary teeth of North American Squirrels. Fig. 1, Syntheosciurus brochus; 
Figs. 2-3, Tamiasciurus hudsomus gymnicus; Figs. 4-5, Sciurus vulgaris leu- 
courus (for comparison); Figs. 6-7, Baiosciurus deppei matagalpe; Figs. 8-9, 
Echinosciurus aureogaster hypopyrrhus; Figs. 10-11, E. poliopus cervicalis; 
Figs. 12-13, Neosciurus carolinensis carolinensis; Figs. 14-15, Hesperosciurus 
griseus griseus; Fig. 16, Otosciurus aberti aberti; Figs. 17-18, Parasciurus niger 
rufiventer; Figs. 19-20, P. arizonensis arizonensis; Figs. 21-22, P. apache; 
Fig. 23-24, P. oculatus oculatus. 
VII.— Skulls of South American Squirrels. Figs. 1-3. Nannosciurus whitehead 
(for comparison); Figs. 4-6, Microsciurus similis similis; Figs. 7-8, Leptosciurus 
pucheranit pucheranti; Figs. 10-12, L. ignitus irroratus; Figs. 13-14, L. leu- 
cogaster. 
VIII.— Skulls of South American Squirrels. Figs. 1-8, Mesosciurus hoffmanni hoff- 
manni; Figs. 4-5, M. gerrardi gerrardi; Figs. 7-8, M. saltuensis bonde; Figs. 
9-10, M. gerrardi miller. 
IX.— Skulls of South American Squirrels. Figs. 1-3, Notosciwrus rhoadsi; Figs. 4-6, 
Guerlinguetus estuans estuans; Fig. 8, G. estuans gilvigularis; Figs. 9-10, G. 
ingram. 7 
X.— Skulls of South American Squirrels. Figs. 1-3, Urosciurus tricolor; Figs. 4-6, 
U. duda. 
XI.— Skulls of South American Squirrels. Figs. 1-3, Urosciurus pyrrhonotus pyrrho- 
notus; Figs. 4-6, U. langsdorffit langsdor ffir. | 
XII.— Skulls of South American Squirrels. Figs. 1-8, Semosciurus stramineus stra- 
mineus; Figs. 4-6, S. flammifer. 
XIII.— Maxillary teeth of South American Squirrels. Figs. 1-2, Nannosciurus 
whiteheadi (for comparison); Figs. 3-4, Microsciurus similis simiiis; Figs. 5-6, 
Leptosciurus pucheranii pucheranii; Figs. 7-8, L. ignitus wroratus; Figs. 9-10, 
L. leucogaster; Figs. 11-12, Mesosciurus hoffmanni hoffmann; Figs. 13-14, 
M. gerrardi gerrardi; Figs. 15-16, M. saltuensis bonde; Figs. 17-18, M. gerrardi 
