266 DESCRIPTION OF A COLLECTION OF FOSSILS, 



Gault, but has a very different septum ; the tubercles on the dorsal angles are 

 more numerous and alternate instead of being opposite, and on the sides the 

 tubercles are fewer and more isolated. It also has fewer ribs. I sent this shell, 

 with several other doubtful Ammonites, to Prof. Alph. Hyatt, who has named a 

 number of species of the genus from South America. His descriptions are, how- 

 ever, so unsatisfactory that, as in this and the other cases where I have his species, 

 I was unable to identify them. For this reason, therefore, I do not hesitate in re- 

 describing the species and figuring it, so as to enable those who follow us to better 

 recognize it. His note accompanying the specimen is as follows: "This is my 

 Buchiceras attenuatum from Celedin, Peru, but the specimens described by me 

 Avere smaller and younger." There are some strongly-marked points of difference 

 between my specimen and the few characters pointed out by Prof. Hyatt, but he 

 seems to consider them the results of difference of age. 



In not following Hyatt, Waagen, and others in the generic subdivisions of the 

 Ammonites, I must admit that I am not yet convinced of the utility of the proposed 

 genera. In the present state of zoological classification it has become clear that 

 trenchant generic, or even specific, lines cannot be drawn ; in other words, with 

 full series of specimens, genera and species resolve themselves into convenient 

 groups, between which transitional forms occur. A genus can no longer be con- 

 sidered "a group of species, having a series of characters in common, and by which 

 it can be distinguished from every other group." Rather, it is a group of species, 

 most nearly allied to some one typical form — in short, a pure matter of conve- 

 jiience — and since ideas can only be expressed by words, these groups must have 

 names which, for convenience, we call generic names. Now, in the Ammonites it 

 may be very well to group the species together, and sections in the genus, whether 

 known as "sections," "sub-genera," "groups," or what not, are undoubtedly use- 

 ful; but it seems to me unnecessary to burden our already ponderous nomenclature 

 with perhaps a hundred more names, when one will suffice. The transitions from 

 one of the new genera to another are so gradual, so minute and perfect, that they 

 unnecessarily increase the labor of the student, instead of simplifying it; and the 

 prime object of classification is to obviate this. The best proof of this last asser- 

 tion is that no two of the leaders of the new system agree on the course to pursue, 

 or on the limits of the genera proposed. I might add much with reference to the 

 genera of the Ammo?iitidce, based on the manner of coiling. It is generally recog- 

 nized that these genera are purely artificial, and that species are well known, 

 especially in Europe, belonging at the same time to several genera. But this 

 subject is foreign to the present paper, and I know that it is in better hands than 



