Io6 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



fossils. Such marks are the sutures, the shape of the whorl, 

 and surface ornamentation. Then, too, the ammonoids in 

 growth envelop and protect the chambers of the earlier 

 stages, thus preserving in a single individual a complete 

 record of their larval history. By pulling off these outer 

 coils the naturalist can obtain the shell in any desired stage, 

 and can prevent the possibility of mistakes by selecting 

 adults to start with. A study of the ontogeny of a fossil 

 ammonoid may thus be carried on with as great accuracy 

 as if the naturalist could hatch out and bring up the young 

 animal in a marine laboratory. 



Many authors have worked on the phylogeny of Mesozoic 

 ammonites, and Hyatt has used especially the comparison of 

 stages of growth of the individual with successive genera 

 and species. But Mesozoic forms are so far from their 

 origin that their ontogeny is long and the meaning of larval 

 stages obscure. If we wish to learn the history of the race 

 we must go back to the ammonoids of the Paleozoic, the 

 goniatites. These forms, being nearer their origin, have 

 shorter larval periods and go through fewer stages of growth ; 

 their interpretation is therefore simpler. Branco accumu- 

 lated a considerable mass of exact data on the ontogeny of 

 several goniatites, but without correlating these stages with 

 genera. His figures are just as good and reliable as if he 

 had done so; but since he was not looking for certain stages 

 of growth, often the very ones we should like most to see 

 have not been figured, due no doubt to lack of specimens. 

 Karpinsky, in the same way, has worked out the ontogeny 

 of Pronorttes and Medlicottia, and the phylogeny of the 

 ProlecanitidcB. Outside of this work the ontogeny of the 

 goniatites is unknown, and they have been grouped together 

 arbitrarily, often in contradiction to their true relationships. 

 Probably so little work has been done in this line because 

 of scarcity of specimens, especially such as can be taken 

 apart to expose the larval stages. Paleozoic rocks have 

 nearly everywhere been subjected to alteration and defor- 

 mation, so that while species can be described from material 

 found in them, it is rarely that one finds the inner whorls 

 well preserved in cephalopods. 



