22 CARBONIFEROUS AMMONOIDS OF A^NIERIC'A. 



few phyla recognized. Since most of tlie ammonoid genera of the 

 Devonian and Carboniferous were progressive, and probably gave rise to 

 descendants in the Permian and Mesozoic, there ought to be nearly as many 

 phyla, or genetic series, as there are primitive genera. But since some of 

 these are nearer of kin than others, for the sake of convenience we group 

 them together, in spite of the fact that this does not express the true filiation 

 of the genera. Thus, even at the best, many of the so-called families will 

 not be a true genetic series, but a group of nearly related morphological 

 equivalents. It is doubtful whether the ideal of strictly monophyletic fiim- 

 ilies and genera can ever be realized, even if the geologic record should 

 turn out to be less broken than we now suppose it to be. Of the great 

 majoi'ity of Paleozoic ammonoids we do not now know, and probably shall 

 never know, the ontogeny, and until we are able to compare in every case 

 the individual ontogeny with the supposed genetic succession as preserved 

 in the rocks we can never hope to establish a classificatiou that will not be 

 overthrown by each discovery of new faunas. 



One great difficulty in classification is that we do not yet know what 

 characters are of fundamental importance in taxonomy. One systematist 

 selects the length of the body chamber as the criterion, another the septa, 

 another the sculpture. A rigid adherence to any one of these systems 

 leads to absurdities, for it_ becomes clear that any one of these characters 

 may appear at different times in different stocks; and a dependence on any 

 one character would cause the grouping together of forms that have no real 

 kinship. The only safe way is to take into consideration all these characters, 

 where it is possible, and to compare in every case the individual ontogeny 

 with the biologic sequence as preserved in the successive geologic forma- 

 tions. The writer has endeavored to do this in the classification ndopted 

 in this work. 



TABLE OF PALEOZOIC AMMONOID GENERA. 



For convenience of reference there is given below a table showing tlie 

 genera and families now known from the Paleozoic, and their geologic 

 range. This is based on the works of Hyatt, Gemmellaro, Karpinsky, 

 Freeh, Waagen, von Mojsisovics, von Arthaber, Haug, and Diener, and 

 on the writer's own studies in the ammonoids of the Carboniferous and 

 Lower Trias. This classification is only tentative; it represents merely 

 the present state of knowledge, or rather of opinion, concerning the deri- 



