86 



continuous : upper posterior molars (M 2, 3) eaca with a shal- 

 low valley extending inwards from the anterior portion of the 

 inner wall, and with two or three deep depressions in the 

 inner half: lower molars (PM 3, M 3) with two (anterior 

 and posterior) more or less defined crescent-shaped ridges: 



canines small. 



MACKAUCHENIIDAE. XLIX.) 



** Skull with the basioccipital comparatively narrow forwards : 

 with the nasal hones produced forwards and terminating in 

 a free narrowed surface; the supra-maxillary bones with an 

 upward developed expansion (connected with the nasal 

 bones) and widely separated above in front. Dental series 

 interrupted by wide diastemas: upper molars (PM 2, M 1, 2, 

 3) each with a deep valley extending obliquely inwards from 

 the median portion of the inner wall and a shallow one ex- 

 tending from the angle or posterior wall : lower molars (PM 

 2, M 2) with two (anterior and posterior) crescent-shaped 



ridges: canines well developed. 



PALAEOTHEEIIDAE. (L.) 



b. Upper (as well as lower) true molars without a continuous outer 

 wall, but (M 2-3, at least,) each with two complete transverse 

 crests. (Lophiodontoidea.') 



1. True molars as well as pre-molars in part (PM 2, 3, 4) nearly 

 similar, squarish, and each with the anterior crest marginal, but 

 with an anterior cingulum terminating in a cusp at the antero- 

 outer angle of the tooth ; hindmost molar (M 3) with no posterior 

 lobe. Anterior feet with four toes ; posterior with three, (in 



known types). 



TAPIKIDAE. (LI,) 



2. True molars and pre-molars differentiated from each other ; the 

 former oblong, with the anterior crest remote from the anterior 

 margin and continuous with a small crest recurrent from the 

 outer wall : hindmost molar with a posterior lobe ; (pre-molars 

 not bilophodout but with a lobe extending inwards from the 

 inner wall). Anterior feet with lour (?) toes; posterior with 



three (?). 



LOPHIODONTIDAE. (LID 



B. Nasal region compressed and extended forwards, the supramaxil- 

 lary bones excluded from the nasal apertui'e ; the nasal bones 

 elongated and extending far forwards, and articulated with the in- 

 termaxillary bones. Molars (M 1 , 2, 3) of upper jaw each with two 

 transverse rows of tubercles (3|3) separated by a transverse valley 

 and with a cingulum anteriorly and internally: (lower molars dis- 

 similar). (Pliolophoidea.) 



PLIOLOPHIDAE. (LIII.) 



