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PROCEEDINGS OF THE NATIONAL MUSEUM 



of the teeth agree with Matthew's (1918, p. 583) figures of D. 

 ahsarohae. 



Altliough this skull is very badly broken and crushed, it adds a 

 few details to our knowledge of the genus. Because Icto'ps is relatively 

 well known, comparisons will be made with it, although the two 

 forms are not closely related : 



(1) The frontonasal suture lies a short distance in front of the 

 orbit. (2) The zygoma is a little heavier than in Ictops. (3) Post- 

 orbital process is short but very well defined. A companion process 

 was not observed on the fragment of the zygoma preserved. (4) The 

 orbit appears to be as large relatively as in Ictops. (5) The sagittal 

 crest is single and moderately high. (6) The parietal foramen appears 

 to lie closer to the crest than to the squamosal. (7) Squamosoparietal 



Fi( 



76. 



-Didelphodus ventanus Matthew, U.S.N. M. No. 18369; occlusal view of left 

 P2-M3, X4. 



foramina were not observed. (8) The union of the mastoid portion 

 of the petrosal and the squamosal appears to have been similar to 

 that in Ictops. (9) The mastoid appears to form as much of the 

 occiput as in Ictops. (10) The relationship of the glenoid to the 

 periotic suggests that the postglenoid and posttympanic processes 

 of the squamosal were separated by a meatal iiotch, although these 

 processes were broken away. (11) The tympanic ridge of the ali- 

 sphenoid is lacking, but there is a short one on the glenoid portion 

 of the squamosal. (12) The foramina in the alisphenoid appear to 

 have been much the same as in Ictops, but this region is badly crushed 

 and difficult of interpretation. (13) The alisphenoid appears to be 

 fused to the basisphenoid. (14) The periotic appears to be rather 

 large judged by the dimensions of the skull that can be observed. 

 (15) The inferior border of the massateric fossa is sharply defined 

 by an abrupt indentation as in Deltatherldium. 



MEASUBEMENTS OF TEETH OF DIDELPHODUS VENTAKUS (IN MILLIMETERS) 



Len^h Width 

 pa-M' 13.5 



M'-;* 



Diastema P- 

 P2 



P3 



P* 



Ml 



M2 



M3 



8.0 



