32 



MAMMALIA 



CLASS V 



of the lower jaw infledecl. Condyle not sharpkj distinguished from the angle. 

 Coronoid process broad. Dental succession restricted to last P. Jura of England 

 and North America. 



Triconodon Owen (Triacanthodon Owen) (Fig. 50). 



? 1.4.3-4. 



Upper C 



3.1.4.3-4. 



with two roots. P with small fore and hind cusp, if with three cusps of 

 almost the same size. Purbeck beds of England. 

 Priacodon Marsh. Upper Jura of Wyoming. 



^^ms^^-^A 



Fig. 50. 



THconodon mordax Owen. Purbeck strata of Durdlestone Bay, Dorset. A, Lower jaw, i/j (after Owen). 

 B, Upper jaw dentition and lower jaw, 2/j. Restoration. (After Osborn.) 



Amphilestes Owen. 



P and M differing but slightly. Middle 



4.1.4.5. 



cusp higher than those in front and behind. Great Oolite ; Stonesfield, 

 England. 



PhascolotJierinm Owen. ■ ^ , ^ . Behind the C a diastema. Central cusp 

 4.1.3.0. ^ 



of P and ilf higher than side-cusps. Great Oolite ; Stonesfield, England. 



Menacodon Marsh. . Secondary cusps smaller than primary cusp 



and slightly inflected. Upper Jura ; Wyoming. 

 Tinodon Marsh. Upper Jura ; Wyoming. 



Spalacotheriiim Owen. 



3.1.4.6. 



Purbeck ; England. S. tricuspidens Owen. 



Family 3. Pantotheriidae (Trituberculata Osborn, Pantotheria Marsh). 



Small insectivores, having the lower jaw without inflected angle, with primitive, 

 tuherculo-sectorial loiver M and trituhercular iipper M. Lower I usiially forwardly 

 inclined, P^ and P^ larger than M. Generally eleven teeth, 4 P, 7 M, following 

 the canine. Jura and Upper Cretaceous of England and North America. 



These small forms, restricted to the late Mesozoic, are referred to the 

 Placentalia by Osborn. Nevertheless it cannot be denied that certain of these 

 represent the ancestral forms from which the Insectivora and Creodontia are 

 descended. At the same time they are related to Triconodontidae, and also to 

 Myrmecohius. The latter form is clearly marsupial, notwithstanding the 

 slightly inflected angle of the lower jaw. The large number of M is sufficient 

 reason for placing it among the latter forms. The trigonid of the lower M, 

 arising from the protoconid, paraconid and the metaconid, is well developed ; 

 the talonid, however, is still very small and is represented only by a single 



