230 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxx. 



the face. Nasals somewhat expanded posteriori}'. Tympanic bullae 

 not ossified. Teeth 44 in number, the molars tritubercular above, 

 tuberculo-sectoriiil below, the premolars trenchant. Ribs short, ster- 

 num narrow, tail long and powerful, limbs rather short, flexible, feet 

 pentadactyl, pollex and hallux divergent, centrale present, astragalus 

 with shallow trochlea and round convex head; fibula little reduced, and 

 ulna as stout as radius. Coracoid process on scapula. 



Primitive eutherian features. — Dentition gxiis- Angle of jaw not 

 inflected. Sacrum of 3 vertebrae. No vertebrarterial foramen on 

 seventh cervical. 



Primitive carnivore features. — Incisors small, canines large, piercing. 

 Parietal ))ones long, basicranial region long, mastoid exposure small, 

 lateral. Posterior nareal canal long and deep. No false (alisphenoid) 

 bulla. Dorsolumbar formula twenty. Lumbars very large and long, 

 their zygapophyses large and very convex. Ungual phalanges bear- 

 ing moderately compressed claws. A small contact between astragalus 

 and cuboid. A third trochanter rather high up on shaft of femur. 



Cursorial a<htj>tati<ms. — Limb V)ones elongate. Scapula long and 

 narrow. Humerus with reduced deltoid and supinator crests. Ulna 

 and radius with limited amount of pronation and supination. Carpus 

 broad, its proximal articulations transverse. Ilium expanded, distal 

 end of femur deep, astragalar trochlea somewhat excavated and 

 extended posteriori}', and head somewhat deepened. Fore and hind 

 feet somewhat compressed and apparently digitigrade. 



Special lty<vnodont c/ui/'acfcrs. — Molars developing a shear by exten- 

 sion of parastyle, especially on M f . Manus and pes mesaxonic. A 

 fibulo-calcaneai- facet. Astragalo-cuboid facet reduced. Claws fissured 

 (also in Mesonj-chidie and Oxya^nida^). 



Generic and speciHc characters. — These need not be repeated here, 

 as they have been fully defined in an earlier section of this paper. 



RELATIONSHIPS OF SINOPA. 



The primitive mammalian features are predominant, as might be 

 expected in a Middle Eocene animal. These features are found in all 

 early mammals, whether Metatherians or I^utherians. Sinojya is, how- 

 ever, a typical Eutherian in the dentition, in the conformation of the 

 angle of the jaw, and other characters of less importance. The primi- 

 tive carnivore features are numerous and important, and amply dem- 

 onstrate the pertinence of Sinopa to this order. The characters of 

 the base and back of the skull especially distinguish it sharply from 

 either marsupials or Insectivora. The cursorial adaptations in the 

 limbs and feet are comparatively slight, but unmistakable. Along 

 with the special hyienodont characters they demonstrate the position 

 of the genus as a primitive member of the HyaMiodontidic. It stands 

 directly ancestral to Ilijivnodon in all details of its structure and shows 



