SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 349 



for lodgement of the vermis and lateral hemispheres of the cerebellum are 

 proportionately as large as in Thylacynus. The olfactory sinuses are 

 enormously developed, indicating the possession of keen powers of scent. 

 The ascending processes of the premaxillae are shorter than in the other 

 Santa Cruz genera. The nasals are greatly expanded posteriorly, occu- 

 pying almost the entire width of the interorbital tract and excluding from 

 contact the frontals and maxillae. The frontals between the orbits are 

 plane in B. tuberata, slightly convex in B. excavata. Postorbital frontal 

 processes are entirely wanting and the temporal ridges poorly defined. 

 The sagittal crest is lower than in Thylacynus ; its free border is concave 

 in profile. The supraoccipital is not exposed on the upper .surface of the 

 skull, the parietal extending to the margin of the lambdoidal crest as in 

 Prothylacynus. The orbits are smaller than in Thylacymis and are placed 

 farther forward. A large lachrymal tubercle is present on the orbital rim. 

 The lachrymal duct opens well within the orbit. A small foramen pierc- 

 ing the facial expanse of the lachrymal in B. excavata (PI. XLV, fig. i) 

 may possibly be homologous with the external opening of the lachrymal 

 duct in Thylacynus. The zygomatic arches are heavier and more widely 

 expanded than in Thylacymis. The postorbital jugal processes are smaller 

 and the preglenoid processes larger than in the latter genus. 



The occiput (PI. XLVI, fig. 4) is semicircular in outline and in B. 

 excavata does not project posteriorly beyond the condyles, which differ 

 from Thylacynus in being wider superiorly and more obliquely placed. 

 The areal extent of the mastoid on the lateral border of the occiput is 

 proportionately less than in the recent genus. 



' The base of the skull is fairly well preserved in the specimen of B. 

 excavata (No. 15, 120, PI. XLIV). .The basioccipital and basisphenoid are 

 almost flat. The paroccipital processes are short, resembling Prothyla- 

 cynus rather than Thylacynus. The large condyloid foramen is preceded 

 by an accessory foramen of approximately the same size. The auditory 

 region resembles Prothylacynus in the absence of alisphenoid dilatation, 

 but the foramen ovale does not pierce the alisphenoid opposite the glenoid 

 cavity, as in the latter genus, the posterior branches of the fifth and 

 seventh nerves probably emerging between the alisphenoid and the tym- 

 panic. The latter element has been shed, exposing the petrous, which is 

 smaller than in Pyothylacynus. The palate is without vacuities, but is 

 pierced by a number of accessory palatal foramina. The anterior palatine 



