1920] 



Stock: An Early Tertiary Vertebrate Fauna 



273 



area for the masseter muscle is more sharply defined than in jaws of 

 the Recent series and forms a V, the arms of which are separated by 

 an acute angle. In jaws of the Recent CiteUus the anterior border of 

 the masseteric fossa is rounded and the upper portion is not so sharply 

 defined as in no. 23611. In the latter specimen, also, the anterior end 

 of this area extends forward to a point below the middle or anterior 

 end of My, whereas in Recent jaws the area reaches to a point below 

 P^. There appears to be a little variation in forward extension of tliis 

 fossa in the Recent Citcllus, but it is always somewhat more advanced 

 than in the specimen from Tecuja Caiion. 



Fig 6. Sciui'id, sp. indet. Fragment of mandible with Mj and Mj, lateral 

 and occlusal views, x 2. Red beds, Tecuja Canon, California. 



Mj and Mj are well worn. A small cuspule is present on the inner 

 side of the occlusal surface of each tooth between the anterior and 

 posterior cusps. This cuspule apparently occurs but rarely in the 

 corresponding teeth of the Recent CiteUus from California. 



Age and Relationships of Fauna 



From a consideration of the marine invertebrate fauna secured 

 from the upper division of the San Lorenzo in the region west and 

 northwest of Tecuja Caiion, B. L. Clark'' is of the opinion that a faunal 

 stage is represented which may be younger than that of the IMolopo- 

 phorus lincolnensis zone of the Oligocene of Washington, and is pre- 

 sumably close in its relationship to the fauna of the Agasoma gravidum 

 zone of California as developed in the vicinity of IMount Diablo. It 

 appears evident that the uppermost stage of the marine Oligocene, the 



Personal communication. 



