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) 



ANCHITHERIIDAE. (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. (Rhinocerotoidea.) 



aa. Neck abbreviated. Incisor teeth (attypically) reduced ia 

 number or entirely suppressed. (Rhinocerotoidea 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, M 3) with two curved transverse 



crests. 



RHINOCEROTIDAE. (XLVIIL) 



bb. Neck more or less elongated. Incisor teeth developed in 

 normal number (;). (Rhinocerotoidea 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 



