SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 397 



present, in contrast with the double condyloid foramen so common among 

 existing marsupials. The tympanic (PI. LIX, fig. 2) is . annular and 

 unfused with the adjacent bones of the skull. The alisphenoid is dilated 

 to form the auditory bulla. As this region is imperfectly preserved in all 

 the specimens examined, it can not be satisfactorily determined whether 

 the petrous was involved in the formation of the posterior portion of the 

 bulla, as it is in Dasyums and Microbiotherium. The basisphenoid is 

 ridged, as in existing carnivorous marsupial's. Prominent alisphenoid 

 ridges extend posteriorly to the confluence with the auditory bullae. The 

 pterygoids are not preserved in any of the specimens examined and 

 were probably small and scale-like. The posterior nares terminate either 

 opposite or slightly posterior to the last molar. The palato-narial border 

 is thickened, resembling the corresponding region in the skull of Dasyums, 

 and is more or less emarginate, varying slightly in the degree of develop- 

 ment of the median process in different individuals of the same species. 



The palate is long and triangular in shape, increasing in width pos- 

 teriorly. Palatal vacuities are conspicuously absent. The incisive fora- 

 mina terminate a short distance posterior to the premaxillary suture. A 

 large foramen perforates the palatal surface of the maxillary opposite either 

 canine. Accessory palatal foramina are less numerous than in Borliyccna. 

 The margins of the palate are depressed for reception of the tips of the 

 lower molars, when the mouth is closed. The posterior border of the 

 palate is perforated by a large foramen on either side of the nares, as 

 in nearly all marsupials. 



With a few important exceptions, the cranial foramina are the same in 

 number and position as in existing carnivorous marsupials. As already 

 noted, the condyloid foramen is single. The basisphenoid has but one 

 perforation, that for the internal carotid artery. The foramina of the lateral 

 sinuses are especially well developed. The postglenoid and sub-squa- 

 mosal foramina are the largest. The postzygomatic, which opens ante- 

 riorly within the lip of the postglenoid foramen, varies in size in different 

 individuals of the same species. A small foramen occasionally pierces' 

 the jugal process of the squamosal just above the glenoid cavity. 



The mandible is slender, with moderately convex inferior border. The 

 coronoid is less strongly inclined posteriorly than in Tliylacynus, resem- 

 bling rather the condition in Dasynrus. The masseteric fossa is broad, 

 with prominent borders. The condyles have about the same degree of 



