84 NEW YORK STATE MUSEUM 



or conchiolinous substances, with which some have compared these 

 pigments, would have been destroyed long ago. Especially in the 

 present case, where the etching of the shell has been able to destroy 

 only the lighter bands, it would seem that melanin pigments that are 

 characterized by their resistance to acids, must be present. 



The greater resistance of the color bands to solution and weather- 

 ing has, as stated before, been also observed by Foerste. The fact 

 that also in all cases of color banding observed by Foerste, this band- 

 ing consisted of various tints of brown, suggests that all these color 

 bands consisted of melanin, perhaps in association with iron 

 (see Oppenheim, op. cit. p. 391). Em. Kayser's experiments 

 in the Devonian brachiopod Rhynchonella pugnus 

 indicate that also there a melaninlike pigment in chemical combina- 

 tion with iron is in evidence. 



The new and important feature in the Trenton limestone speci- 

 mens before us is the fact that the color bands are present on one 

 side of the conch only, the other side having been entirely white. 

 We see in this phenomenon direct evidence that the species in ques- 

 tion, Geisonoceras tenuitextum, was given either 

 to crawling upon the bottom of the sea, or to swimming in a horizon- 

 tal position; either of which habits would develop a differential color- 

 ing on the dorsal and ventral sides, the former assuming a darker, 

 the latter a lighter color. It seems improbable that the long and 

 straight cones could have been carried horizontally in swimming, 

 especially as these cephalopods must be assumed to have, like all 

 their recent descendants, swum backward by the expulsion of water 

 from the f orvvardly directed funnel. The often delicate shells could 

 not have stood the shock of frequent impacts incidental to such mode 

 of propulsion, and the prevailing preservation of the acute apex of 

 the conchs militates against the view that such impacts could actually 

 have occurred at frequent intervals. It is therefore more probable 

 that the conchs, buoyed up by gas in the air chambers, were lightly 

 dragged over the soft mud of the bottom, by the probably sluggish 

 animals. 



There are several other observations that support this conclusion. 

 The most important is that the conchs on closer inspection turn out 

 not to be regular cones, but to be slightly curved so that the side 

 with color bands (dorsal side) is slightly convex, while the other is 

 straight or even a little concave. This feature, distinctly observable 

 by holding a ruler against any part of the dorsal or ventral side, is too 

 regular to be due to postmortem compression or fracturing. 



