L. F. Spath — Notes on Ammonites. 177 



Aninionoid animal to its shell afforded important characters for the 

 purposes of classification, but both on account of the comparative 

 scarcity and the indefinite nature of these impressions they have not 

 proved of value yet in the classification of Ammonites. 



On the whole, then, the Ammonoid suture-line may be considered 

 to be a more useful feature for classificatory purposes, especially of 

 the larger groups and families, than any of the above characters, 

 though, like any other character, it cannot be used by itself as the 

 sole basis for the natural classification of organisms that are made up 

 of an almost infinite number of characters, each of which is in a con- 

 tinuous state of movement, either originative, progressive, or 

 retrogressive. 1 Holzapfel 2 stated long ago that one single character, 

 such as the shape of the first suture, the direction of the siphonal 

 funnel, or the shape of the peristome, cannot well be used for 

 classification. In his paper on the genus Oppelia 3 Wepfer stated: 

 " In palseontological works the question is often asked, which 

 characters in Ammonites are decisive, the lobes, the length of the 

 body-chamber, etc., etc. ? I believe they all are, to a certain extent' 

 but one cannot formulate general rules. All characters are liable to 

 variation, and what decides is the general appearance, at any rate we 

 get further with this than with following some one-sided character." 

 Hyatt's classification of the Nautiloids 4 according to the structure of 

 the septal neck, though more attractive than the previously existing 

 classifications, cannot be really natural, and when it is found that 

 Hyatt 5 included, e.g., in his family Estonioceratidae, based on the 

 shape of the whorls, beside the Ordovician genus JEstonioceras, also the 

 Jurassic Digonioceras, that is two genera that almost certainly have 

 not the remotest affinity, the artificial character of his classification 

 becomes evident. The same applies to his classification of 

 Ammonoidea, as is shown, by the inclusion in, e.g., his Leptocampyli 

 of such a heterogeneous mixture of Ammonoids belonging to widely 

 removed stocks, or his separation of such closely allied genera as, e.g., 

 Reinecheia and Erymnoceras, Sigaloceras and Kepplerites, not only 

 into different families, but even different super-families. 



It seems to the writer that the development of the Ammonite 

 suture-line has to be studied from its first "angustisellate" beginning, 

 and used as a basis for classification only in conjunction with the 

 development of all the other characters of the shell. The use for 

 geueral classification of, e.g., the symmetrical or asymmetrical 

 arrangement of the first lateral lobe, the changing width of the 

 external saddle, the number of auxiliary lobes, or any other similar 

 peculiarity of the suture-line, by itself, is unsatisfactory. 



1 H. P. Osborn, "Origin of Single Characters as observed in Fossil and 

 Living Animals" : Presidential Address Pal. Soc. Amer., 1914 (see Nature, 

 November 11, 1915, pp. 284-5). 



3 "Die Cepbalopoden-fiihrenden Kalke d. Unt. Carbon v. Erdback- 

 Breitscheid bei Herborn " : Pal. Abb. v. Dames u. Kayser, vol. v, No. 1. 



3 Loc. eit., 1912, p. 30. 



4 The Genera of Cephalopods, etc., 1883. 

 3 In Zittel-Eastman, op. cit., 1900. 



DECADE VI. — VOL. VI. — NO. IV. 12 



