1876.] " 363 [Hyatt. 



of different values in different groups, and the attempt to use it with 

 the same meaning in every group results, as in all other cases, in 

 confusion. Thus in Waagen's diagnoses of the genera Stephanoce- 

 ras, Perisphinctes and Kosmoceras, we find that they are all three 

 described as having " simple (entire) mouth-openings or ears." In 

 each genus the characteristics of the Aptychus are the same, as 

 stated by Waagen, and each has the same variability in the outlines 

 of the mouth. These surely will not suffice to distinguish them, 

 since they are precisely the same in each genus, and we have to fall 

 back on the length of the living chamber or the comparative length 

 of the animal and shell. 



I do not mean to be understood as denying the existence of natu- 

 ral sub-groups of generic value, for undoubtedly such do exist, and 

 some of them must bear Waagen's names in nomenclature, but 

 merely to point out the inapplicability of such characteristics as he 

 has arbitrarily employed to distinguish them. In many other groups 

 the outlines of the mouth are exceedingly constant, as in the Arie- 

 tidae, and are very properly used to designate them in common with 

 other characteristics. 



I allude principally to these three characteristics, the Aptychus, 

 the length of the living chamber and the mouth outline, because it is 

 only in the application of these that Waagen differs from other natu- 

 ralists, especially in the former, since Suess applied the two latter 

 to the distinction of his genera Lytoceras and Phylloceras. 



Such differences in the views of Paleontologists as are above alluded 

 to, lie deeper, however, than any such contrasts in the translation and 

 application of facts. They rest upon the different modes of study, 

 which distinguish two schools of Naturalists. In one school the 

 effort is being perpetually made to discover some set of characteristics 

 by which animals may be distinguished one from another. Every new 

 organ, or indication of such, when discovered, is applied at once to 

 the definition of groups, as if this was the great object of all classifi- 

 cation. The distinction of groups from each other doubtless repre- 

 sents to a certain extent our knowledge of their organization, but 

 only in proportion to the number of the parts or characteristics which 

 may be employed in classification. Consequently arbitrary classifica- 

 tions based on single characteristics are the most imperfect, since they 

 necessarily leave out of consideration the numberless affinities of the 

 groups, and all the minor points of difference which here and there 

 appear. 



