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evolution is towards closer coiling of the shell and in retrogressive 

 series the direction of evolution is towards uncoiling. 



Aturidce. 



In my second paper on l ' Carboniferous Cephalopods," Geological 

 Survey of Texas, Fourth Annual Report, p. 389, I 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 Clymeninae. The forms are compressed and 

 as a rule deeply involute. Unfortunately 1 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 Enclimatoceras 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. 



Aturia Morrissi, Michellotii. 



Loc, Baldasseres, Tertiary. 



PI. 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 gvroceran 

 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 



