L. F. Spath — Notes on Ammonites. 223 



is referred to the old genera " Goniatites" or "Ammonites ", or to 

 a modern small subdivision. For stratigraphical purposes a much 

 more exact definition than in the past of the horizon of each form will 

 be necessary. Here, again, clearness and uniformity of nomenclature, 

 facilitated by a natural classification, would be of great advantage. 

 Since Mr. Lang 1 has shown that in the case of JDeroceras armatum, at 

 least at Charmouth, there probably is " an example of the zonal fossil 

 lying entirely outside the zone that bears its name", it will be 

 admitted that this revision of the horizons of Ammonites is of 

 importance. Moreover, little value now is placed on specific identi- 

 fications for zoning purposes. With regard to graptolites, Dr. Elles * 

 wrote recently : " Detailed knowledge of the different species is in no 

 way necessar3 r for the recognition of the different horizons. The 

 nature and value of a Graptolitic zone depends on the assemblage of 

 characteristic forms." And with regard to Ammonites, Mr. Buckman s 

 had stated five years previously that " one did not ascertain the 

 date of a deposit so much by the actual species as by the general 

 facies, in the case of Ammonites. Coarse-ribbed Dumortierice, fine- 

 ribbed Dumortierice, Ammonites of aalensis pattern, Opalinoids, 

 showed the dates as well as more exact identifications, because the 

 successive Ammonites of different genera assumed certain develop- 

 mental facies ". 



As important as a revision of nomenclature and horizons seems, to 

 the writer, to be the elucidation of the phylogenetic problems pre- 

 sented by the Ammonites, and the consideration of their evolutionary 

 significance in relation to research done in other branches of modern 

 science. Developmental palaeontological l-esearch has taken an 

 active part in the establishment of modern evolutionary theories, and 

 with Waagen and Blake 4 one may consider "to have here the true 

 basis of palaeontology as an independent science". As Zittel 5 stated : 

 ' ' The character of palaeontological literature has been correspondingly 

 modified; the purely stratigraphical treatment of palseontological 

 results has been held more and more distinct from the biological 

 systematic treatment, and the latter places the genealogical direction 

 of research more and more in the foreground." 



Since the Ammonite animal is unknown, many important factors 

 of evolution can only be imperfectly inferred and not demonstrated 

 by those structures that alone are preserved to us. The writer 

 would favour, for the fossil forms of Cephalopoda, the division into 

 three main orders, without reference to gills. The Eautiloidea and 

 Belemnoidea are outside the scope of the present paper ; with regard 

 to the Ammonoidea, the division into " Ammonitidse " and 

 " Goniatitidae " is, of course, as little justified as was the original 



1 " The Geology of the Charmouth Cliffs, Beach, and Fore-shore " : Proc. 

 Geol. Assoc, vol. xxv, p. 321, 1914. 



2 Proc. Geol. Assoc, vol. xxvi, p. 267, 1915. 



3 "Certain Jurassic [Lias-Oolitic] Strata of South Dorset, and their 

 Correlation " : Q.J.G.S., vol. Ixvi, p. 53, 1910. 



4 "The Evolution and Classification of the Cephalopoda, an Account of 

 Eecent Advances " : Proc. Geol. Assoc, vol. xii, p. 278, 1892. 



5 History of Geology and Paleontology, London, 1901, p. 380. 



