Pie cre Ns SCART bese 
DistRiBuTION. The genus Scaphites belongs to the family Steph- 
anoceratide 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- 
hest 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 wgualis 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. wgualis. 
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. | 
207 
