NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 87 



posteriorly or so concave transversely. The postglenoid process may 

 be more rugged and posteriorly better envelops the postglenoid 

 foramen. The crest posterior to the foramen ovale, though damaged, 

 seems prominently developed but possibly not so compressed trans- 

 versely as in M eniscotherium. Posterior to the position of the exter- 

 nal auditory meatus the mastoid process, which carries a lamina of 

 the squamosal on its anterior face, is much more elongate in an 

 anteromedial -posterolateral direction. Also, the extent of the mas- 

 toid exposed ventrally between the mastoid and paroccipital processes 

 is much greater than in M eniscotherium in the skull that I examined. 

 This, however, is evidently not constant, as Russell, in pointing out 

 the variability of the paroccipital process, has indicated that it is 

 sometimes indistinct and then closely applied to the mastoid process. 

 According to Pearson (1927) the greater part of the paroccipital 

 process is formed of the mastoid. It is apparently never developed 

 as in M eniscotherium. 



The petrous portion of the periotic in Pleuraspidotherium is very 

 differently shaped than in M eniscotherium, as it is broad posteriorly 

 and very rapidly tapering anteriorly. The slenderness of the anterior 

 portion is suggestive of Hyopsodus, although in the latter it is not as 

 broad posteriorly and more smoothly conical. The sulcus facialis 

 would seem rather similar in the two forms, and the aperture for the 

 facial nerve appears similarly situated, although the positions of the 

 fenestrae ovalis and rotunda cannot be precisely determined because 

 of damage to the specimen examined. Posteriorly the facial sulcus is 

 directed downward toward the position of a stylomastoid foramen 

 opposite the posterior extremity of the exposed petrosal, but this is 

 farther back with respect to the medial root or extremity of the mas- 

 toid process than in M eniscotherium. Lateral to the facial sulcus 

 there is much more of an epitympanic recess in Pleuraspidotherium. 

 In M eniscotherium the mastoid portion lateral to the sulcus is essen- 

 tially flush with the medial margin of the squamosal above the external 

 auditory meatus, although separated from it by a groove. 



Medial to the petrosal the lateral portion of the basioccipital is 

 deep and broadly grooved, which forward leads to the foramen 

 lacerum medium. Presumably this was occupied by the internal 

 carotid, as suspected for a rather similar appearing structure in 

 M eniscotherium. 



The limb and foot material attributed to Pleuraspidotherium seem 

 rather condylarthran, certainly not artiodactyl in form, but, as cau- 

 tioned by Pearson (1927), these were not found in direct associa- 



