L. F. Spath — Notes on Ammonites. 225 



subordinate to the super-famity Phylloceratida, which, like the 

 earlier and probably ancestral super-family Glyphioceratida, belongs 

 to some great "phylum" ranging up from the Devonian. These 

 four or five stocks or "phyla", of which one at least begins already 

 in the Silurian, and only one of which transgresses the Trias-Jura 

 border, comprise for convenience the order Ammonoidea. 



In tracing these "phyla", based so far mainly on the adult 

 suture-line, stress will have to be laid on the ontogenetic develop- 

 ment, as has already been pointed out. Branco, 1 as far back as 

 1879-80, had dissected sixty-four species of Ammonites; but with 

 a few exceptions, among which Professor J. Perrin Smith's paper on 

 the " Development of Lytoceras and Phylloceras " 2 may be mentioned, 

 observations on the less obvious features such as the earliest 

 chambers and the gradual development of the various characters, 

 were neglected by palaeontologists. When Michaelski in 1890, 3 

 relying on the differences in the ornament of the inner whorls of 

 the various species of so-called Virgati, separated these into the two 

 genera Olcostephanus and Perisphinetes, he met with opposition, at 

 first, even from A. Pavlow, 4 who wrote, " The older specimens have 

 absolutely the same type of suture and are so much alike in shape 

 and ornament that it is extremely difficult to distinguish them if the 

 ontogenetic development of each cannot be studied." Since then, 

 practically on differences in shape and ornament of the adult shell 

 alone, some twenty new genera have been created for various forms 

 formerly included in Perisphinetes, but the ontogenetic development 

 of most of them is still unknown. The writer's personal research 

 has been connected chiefly with Lias Ammonites, and the study of 

 the ontogeny of most of their principal types has now been 

 concluded. The phylogenetic conclusions arrived at differ con- 

 siderably from the interpretations of the relationship of these 

 Ammonites given by other authors, and prove that until the 

 development of the more important types at least of other periods as 

 well has been studied in detail, there seems little hope of arriving 

 at a satisfactory classification of Ammonoidea. 



In conclusion, the writer would like to express his obligation to 

 all those who have helped him with material for research or with 

 valuable suggestions. His thanks are especially due to Dr. A. 

 Smith Woodward, the late Mr. G. C. Crick, and Dr. W. D. Lang, 

 of the British Museum (Nat. Hist.); also to Dr. Wyatt Wingrave, 

 Dr. A. Morley Davies, and Mr. C. P. Chatwin. 



" Beitr. z. Entwicklungsgesckichte der Fossilen Cephalopoden " : 

 Palaeontographica, vol. xxvi, pts. i, ii, 1879. 



2 Proc. Calif. Acad. Sci. [3], i, 1898. 



3 "Die Ammoniten der Unt. Wolga-Stufe " : M£m. du Comite Geol. 

 St. Petersbourg, vol. viii, No. 2. 



4 In Pavlow & Lamplugh, Argiles de Speeton, etc., Moscow, 1892, p. 114. 



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