BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 32, PP. 315-320 SEPTEMBER 1, 1921 



PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



OBSERVATIONS ON TTTE MODE OF LIFE OF PRIMITIVE 

 CEPHALOPODS ^ 



BY RUDOLF EUEDEMANN 



[Bead before (lie Paleontological Society Decemher 29j 1920) 



CONTENTS 



Page 



I lulications of a crawling mode of life 315 



u. From color bands 315 



1). From secondary deposits 310 



1 )ifterentiation in size of sexes 317 



Synclironic relation of septa to growth-lines 319 



Interior origin of annulation .320 



Owing to the fact that we have today only the pearly nautilus, a still 

 little known deep-sea form, for comparison, there still exists much doul)t 

 in regard to the mode of life of the Paleozoic Nautiloidea. To cite an 

 example, the simple straight-shelled Orthoceras is considered by some 

 good authorities to have been a bottom crawler, by others as having swum 

 in a vertical position, and by still others as having buried himself in the 

 mud in an upright position, or as having been fixed at the apex. There 

 are few facts known that could shed light on the mode of life of these 

 early cephalopods, and it is therefore thought worth while to record here 

 some new biologic observations on these creatures. 



Ilv^DICATIONS OF A CRAWLING MODK OF LiFE 

 a. FROM COLOR BANDS 



The Trenton limestone of New York has afforded a number of speci- 

 mens of Orthoceras (Geisonoceras) tenuitextum (Hall) that retain red- 

 dish brown color lines on a white background. These lines are found only 

 on one side; they are thickest in the middle of the colored area and be- 

 come separated by wider interspaces in the transitional zones and are 



' Manuscript received by the Secretary of the Society Marcli 3, 1921. 



XXII— BcLL. Geol. See. Am., Vou 32, 1020 (315) 



