563 
evolution is towards closer coiling of the shell and in retrogressive 
series the direction of evolution is towards uncoiling. 
Aturide. 
In my second paper on ‘‘ Carboniferous Cephalopods,’’ Geological 
Survey of Texas, Fourth Annual Report, p. 389, 1 pointed out the 
fact that the genera Enclimatoceras of the Mesozoic, Hercoglossa 
of the Cretaceous and Aturia of the Tertiary formed a distinct 
group by themselves. 
These genera have ventral saddles, deep lateral lobes and lateral 
saddles of so highly specialized outlines that the sutures resemble 
those of some of the Clymeninz. ‘The forms are compressed and 
as a rule deeply involute. Unfortunately I have been unable to 
get the ananepionic substages of Enclimatoceras or Hercoglossa. 
It is, however, fortunate that the involute character of the young 
in these genera and close coiling of adults in the entire group 
makes it highly probable that the young when investigated will not 
be likely to contradict the conclusions obtained from the study of 
Aturia. 
Through the kindness of the Directors of the National Museum 
and Geological Survey and Dr. W. H. Dall and Mr. T. W. Stan- 
ton, I received a number of sections of Hxchmatoceras Ulrichi, 
from Prairie Creek, Wilcox county, Alabama, and Zell county, 
Texas, Tertiary, but not one of these had a centre perfect enough 
to be of any use. 
Aturia. 
This genus, first described by Bronn, has long been admitted and 
is easily recognized by the aid of the peculiar sutures and siphuncle. 
AtTurIA Morriss!, Michellotii. 
Loc., Baldasseres, Tertiary. 
Pl. xiii, Figs. 17-19. 
The ananepionic substage in this species is very globose and the 
growth of the apex is certainly very rapid in all its diameters. ‘This 
rapid increase is, however, not sustained in the transverse diame- 
ters of the metanepionic and succeeding stages. The gyroceran 
bend is so abrupt and the coiling is so close at the end of the meta- 
nepionic, that I have not yet succeeded in seeing and studying the 
dorsum of this substage. The opening of the umbilical perforation 
