316 R. RUEDExMANN MODE OE LIFE OF PRIMITIVE CEPllALOPODS 



entirely absent on the opposite side. The color bands, which probably 

 consisted of melanin pigments, enter the shell substance about one milli- 

 meter deep, and are so resistant to solution and weathering that they 

 have given to many slightly etched shells a fluted appearance, which fact 



has led to the description of a dif- 

 ferent species, Orthoceras strigatum 

 Hall. The color bands lie below the 



Figure 1. — Geisonoceras tenuitextum 

 (Hall) 



Lateral view of portion of concli witli 

 color bands. Natural size. 



fine surface sculpture consisting of 

 intersecting vertical and longitudi- 

 nal lines. 



We see in the phenomenon of the 

 coloring of the shells on one side only 

 direct evidence that the species in 

 question was given either to crawling 

 on the bottom of the sea or to swimming in a horizontal position, either 

 of which habits would have developed a differential coloring on the dorsal 

 and ventral sides. It seems improbable that the long and straight cones 

 could have been carried horizontally in swimming, especially since the 

 creatures, like their descendants, would have swum backward, and thus 

 exposed the delicate shells to frequent collisions 

 and fracturing. 



There is other evidence available that sup- 

 ports the view that the conchs, buoyed up by 

 gas in the air chambers, were lightly dragged 

 over the soft mud by the sluggish animals. One 

 of these is that the shells on closer inspection 

 turn out to be no regular cones, but to be gently 

 curved, so that the side with the color bands is 

 slightly convex, wdiile the other (ventral) side 

 is straight or even a little concave. 



Another observation that corroborates the ex- 

 planation here given is that specimens of the 

 same species found in the Utica shale are some- 

 times overgrown with a bryozoan {S patio pora 

 lineata Ulrich, var. compacta nov.), whose 

 zoarium begins to grow near the apex and thence extends forward toward 

 the aperture of the shell; also on one side of the shell only. If the bryo- 

 zoan had attached itself after the death of the cephalopod, it would 

 hardly have grown pari passu with the shell. 



Specimens of Orthoceras (Protol-ionoceras) trusitum Clarke and Eue- 

 demann from the Guelph limestone at Eochester have also been found to 



Figure 2. — Cyrtocerus par- 



vuluni Barrande, with 



color lianiJs 



Natural size. 



