84 
Titanotherium Leidy. 
Perchoerus Leidy. 
Leptochoerus Leidy. 
Nanohyus Leidy. 
PERISSODACTYLI. 
FAMILIES, 
I. Incisors (4? in lower jaw) in part gliriform, the outer having persistent 
pulps, and growing continuously in a circular direction. (Anchippodonto- 
idea.) 
ANCHIPPODONTIDAE. (XLV. 2.) 
II. Incisors not gliriform. 
1. Middle digit and hoof hypertrophied and alone supporting the body, 
the lateral (second and fourth) digits being more or less atrophied and 
functionless, or (attypically) obsolete (reduced to the condition of 
“splint bones”). Femur with a fossa above the external condyle. 
Skull (attypically) much prolonged forwards. Molars subequal (not 
decreasing forwards) and cuboid; pre-molars (PM 3-4) also enlarged 
(not decreasing forwards) and (except second) cuboid; the second 
(PM 2) elongated; the first milk molar (D 1) more or less persistent 
and not replaced by a pre-molar (PM 1); disproportionately small. 
Incisors with a deep invaginated fold of enamel penetrating the in- 
terior from the crown, and producing a central cavity filled with 
cementum. (Solidungula.) 
A. Ulna with the shaft atrophied and the extremities anchylosed and 
consolidated with the radius. Fibula rudimentary and anchylosed 
to the tibia. Skull with the orbit complete behind. Upper molars 
(PM and M)—at least, of second set—with a deep valley re-entering 
from the postrorse portion of the inner side obliquely forwards, and 
(in connection with a more or less deep valley re-entering from the 
introrse portion of the anterior border or the angle) more or less 
isolating an introrse enamel lobe or area, and with two (anterior and 
posterior) crescentic enamel islands. Lower molars (PM 2, M 2) 
with a valley re-entering inwards from the outer wall, one from the 
introrse portion of the anterior wall, and another (terminating in 
anterior and posterior branches) from the posterior portion of the 
inner wall. 
EQUIDAE. (XLYI.) 
B. Ulna with the shaft complete and moderately developed, and more 
or less differentiated from the radius. Fibula archetypically com- 
plete but archylosed with the tibia. Skull with the orbit incomplete 
behind. Upper molars (PM 3-4 and M) with a deep (anterior) val- 
ley re-entering from the middle of inner side inwards and forwards 
