386 MAMMALIA. 



ing fig. 217 being based almost entirely on the associated remains of one 

 individual. The skull is much elongated, with the usual diminutive brain- 

 cavity and great sagittal crest. The two rami of the mandible are firmly 

 fused together at the syrnphysis, and the angle of the mandible is not 



inflected as in marsupials. The dental formula is .' - - ' and 



i. 3, c. 1, pm. 4, m. 3 



milk-predecessors have been observed in the mandible in connection with 

 the incisors, canines, and all the premolars except pm. 1. The hinderrnost 

 lower milk-molar resembles in shape the relatively small tricuspidate 

 lower m. 1, which is extruded and partially worn before the milk-dentition 

 is replaced. The two upper molars and the lower molars 2, 3, are sharp 

 bilobate cutting teeth, the former with scarcely any trace of an inner 

 tubercle. The canines are much enlarged in both jaws, while the incisors 

 are small and in regular even series. The general proportions of the trunk 

 and limbs are well shown in fig. 217. The humerus has an entepicondylar 

 foramen. The scaphoid, lunar, and central bones of the carpus remain 

 separate in the known American species, but seem to have been fused 

 into a scapholunar element in the European forms. Both feet are penta- 

 dactyl, with powerful claws ; and the animal was probably semiplantigrade. 

 Hycenodon ranges through the Upper Eocene and Lower Miocene both in 

 Europe and North America. The typical species, H. leptorhynchus 

 (fig. 216), and others occur in France in the Phosphorites of Quercy, the 

 Lignites of Debruge, the Paris Gypsum, and in the Lower Miocene of the 

 Puy-de-D6me. Portions of jaws and teeth are also known from the Upper 

 Eocene of Switzerland and of the Hampshire Basin. H. cruentus (fig. 217) 

 and other well-known species are represented by fine specimens from the 

 Lower Miocene (White Kiver Formation) of Nebraska, Montana, and 

 Dakota ; while there is also some evidence of the genus in the underlying 

 Uinta Formation in North America. Detached teeth from the Siwalik 

 Formation of the Punjab, India, have also been provisionally assigned to 

 Hycenodon, but their determination is uncertain. Pterodon is a closely 

 allied genus from the Upper Eocene of France, Switzerland, and the 

 Hampshire Basin, with a third upper molar, and a well-developed inner 

 tubercle on upper molars 1 and 2. 



The representatives of the Creodonts in the Lower Tertiary 

 formations of Patagonia are very remarkable as exhibiting still 

 more resemblance to the carnivorous marsupials of Australia 

 and Tasmania than the animals just described from the northern 

 hemisphere. They have thus been referred to a distinct group 

 termed SPARASSODONTA. Milk-teeth have only been observed 

 preceding one or two of the premolars and the canine ; while 

 there is a distinct inflection of the angle of the mandible, 

 as in marsupials. The palate, however, does not exhibit any 



