85 
and ending in lateral branches, and with a (posterior) valley re- 
entering from the posterior wall. Lower molars with a V-shaped 
valley re-entering from the outer wall, and two V-shaped vallies, 
re-entering from the inner wall (the crowns having W-shaped 
ridges). 
ANCSITHERIIDAE. (XLVII.) 
2. Middle digit and hoof not hypertrophied, and only in connection with 
the lateral supporting the body, the lateral being well developed and 
efficient. Femur without a fossa above the external condyle. Skull 
moderately prolonged forwards. Molars unequal (the first smaller 
than the second), diversiform; pre-molars decreasing in size forwards; 
first milk molar not persistent, but (generally) replaced by a pre- 
molar (PM 1) of moderate size. Incisors without an invaginated fold 
of enamel penetrating the interior. 
A. Nasal region expanded or thrown backwards, the supramaxillary 
bones forming a more or less considerable portion of the border of 
the nasal aperture; the nasal bones contracted forwards, or atro- 
phied. Molars with crowns traversed by more or less well-defined 
continuous ridges. 
a. Upper molars with a continuous outer wall and without com- 
plete transverse crests. (hinocerotoidea. ) 
aa. Neck abbreviated. Incisor teeth (attypically) reduced in 
number or entirely suppressed. (Mhinocerotoidea rhinoceroti- 
formia.) 
* Skull with the basioccipital comparatively well developed 
behind and narrowed forwards; (with tympanic and periotic 
bones anchylosed and wedged in between the squamosal, ex- 
occipital and other adjacent cranial bones.—Huxley;) with 
the nasal bones produced forwards and more or less arched, 
and meeting an upward developed expansion of the supra- 
maxillary bones. Upper molars with a deep valley extending 
obliquely inwards from the median portion of the inner wall 
and (PM 4, M 1-2) a shallow one extending from the posterior 
wall. Lower molars (PM 2, M3) with two curved transverse 
crests. 
RHINOCEROTIDAE. (XLVIII.) 
bb. Neck more or less elongated. Incisor teeth developed in ¢ 
normal number (8). (hinocerotoidea macraucheniformia. ) 
* Skull with the basioccipital widened forwards: with the nasal 
bones extremely reduced and above or behind the orbits: the 
supramaxillary bones rectilinear above, arched and approxi- 
mating each other in front of the nasal aperture but separated 
by the extension upward of the vomer? Dental series almost 
