334 R. S. LULL^ SAUROPODA AND STEGOSAI RIA OF THE MORRISON 



may not include common elements on which to rely, and this is the chai- 

 acter of almost all of the European Sauropod remains. 



On the otlier hand, one highly specialized genns is common hoth to 

 America and Tendaguru, and here the comparison may be based on rela- 

 tively perfect material. 



With the Stegosaurs, opportunity for more perfect comparison lies be- 

 tween Europe and America, but only points to the conclusion that the 

 Morrison beds which contain the American type are relatively newer 

 than those which include the English relatives. 



Correlation based on the Sauropod evidence between Europe and 

 America is not to be relied on at j^resent, but w"e can evidently pornt to 

 the middle Tendaguru horizon of East Africa, which contains the genus 

 common to the Morrison, as homotaxial with the latter. 



As this middle bed at Tendaguru is bounded above and below by marine 

 sediments, the study of their contained faunas, which doubtless can be 

 definitely dated, should serve to determine the age of the ilorrison forma- 

 tion of iSTorth America. From the evidence so far at hand, the age of 

 this zone is certainly not older than uppermost Jurassic, with a decided 

 likelihood that the invertebrate writers will agree on an early Coinanchian 

 (Neocomian) time. 



