THE GENUS SCAPH1TES. 



Distribution. The genus Scaphites belongs to the family Steph- 

 anoceratida) of the order Ammonoidea. The genus includes about 

 forty known species. Its geological range is confined to the Upper 

 Cretaceous Series, but its distribution is widespread, as it is known 

 to have been an inhabitant of at least four continents. The species 

 were no doubt marine littoral organisms. 



The history of the genus forms an interesting record. The ear- 

 liest known species occurs in the Gault of Europe which seems to 

 form a transition stage from the Lower to the Upper Cretaceous, for 

 it is classed by some authors with the former and by others with the 

 latter series. In this earliest known horizon of the genus there are 

 few species, and individuals are not abundant. 



In the formation overlying the Gault, the Cenomian, the primi- 

 tive species, Scaphites cequalis Sowerby, reaches the acme of its 

 abundance. Up to this time, however, few, if any, structural varia- 

 tions have been introduced. But during later Cenomian time disper- 

 sion began and the primitive species made its appearance in the Cre- 

 taceous seas of France and Switzerland. With the migration came 

 new environments which resulted in a differentiation of organic struct- 

 ure, and the consequent production of new species. All of the new 

 species, however, are closely allied to S. ivqualis. 



It is, of course, questionable whether environment is the sole 

 cause of variability. But it is very highly probable that in this case, 

 at least, the change of environment was one of the prime factors in 

 the production of the new species. For it is not improbable that 

 under new conditions bathmism could more readily assert itself. 

 That it did assert itself rapidly is shown by the production, in a short 

 period, geologically speaking, of nearly fifteen species. From this 

 it must at least be inferred that the change in environment gave an 

 impetus to the growth force. It becomes more obvious in the light 

 of the fact that in the center of dispersion but three or possibly four 

 species are recorded for the entire geological range of the genus. 

 Furthermore it is not certain that two of these species did not migrate 

 to the center of dispersion from the Eastern colonies. 



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