222 L. F. Spath — Notes on Ammonites. 



geological occurrence and general resemblance suggest, at least for 

 the Icevigatas group, to which the genus Cymbites should be restricted, 1 

 modification of an Agassiceras development. On the loss of the 

 typical Arietid venter the first lateral lobe tends to assume larger 

 proportions, just as in Oxynoticeras the Arietid suture-line shows an 

 enlarged first lateral lobe and first lateral saddle in compensation for 

 a wide lateral area. Polymorphites, on the other hand, has the first 

 lateral saddle indicated already in the second suture, and though in 

 the later suture-lines, owing to carination and the swinging forward 

 of the umbilical portion, which has been shown to occur similarly, 

 with time, in a number of stocks, the first lateral lobe is smaller than 

 the ventral lobe, the tendency here is in an opposite direction, 

 suggesting a round- ventered, Deroceratid ancestor. 



Even in cases where the suture-line development has been worked 

 out in detail, widely antagonistic explanations of the affinity of the 

 Ammonites can thus be given. Apart from the striking disagreement 

 shown in the classifications of Ammonoids hitherto proposed, there 

 is also the extraordinary increase in the number of genera created in 

 some of these and adding to the difficulties of the student, and it is 

 not surprising perhaps that none of these classifications has found 

 universal adoption. To give an illustration of the divergence of 

 opinion, the four genera Grammoceras, Hudlestonia, Dumortieria, and 

 ffammatocerasjirom the Jurense zone of the Upper Lias, may be taken. 

 Hyatt 8 puts the first and the third into the family Hildoceratidse, 

 and the others into Poecilornorphidae and Phymatoidse respectively. 

 These three families again belong, according to this author, to two 

 super-families, Arietida (the first two) and Phymatoida. Mr. 

 Buckman, 3 on the other hand, puts these same four genera into four 

 families, and only one genus, Grammoceras, is in the same family to 

 which Hyatt had assigned it, i.e. Hildoceratidse. The remarkable 

 part about these four genera, however, is that they are all, and the 

 first three of them closely, allied. This is almost a return to the 

 classifications of the older authors, for, e.g., Pictet 4 in 1854 grouped 

 Ammonites radians, levesquei, and insignis together in "Falciferi". 

 It is not intended to suggest that these old divisions represent natural 

 groups ; but the example tends to show that the scepticism of most 

 general palaeontologists towards the modern classifications of 

 Ammonites was not unfounded. 



A more permanent and uniform classification of Ammonoids may 

 appear desirable to the general palaeontologist and collector who are 

 interested in seeing cleared up the generic nomenclature which, 

 apparently, has drifted into a state of hopeless confusion. Put to the 

 stratigrapher it may still seem of little consequence whether a form 



1 Certain aberrant forms, occurring e.g. in the marmorea and margaritatus 

 zones, and resembling the globosus-lcevigatus group superficially, cannot be 

 included in the genus Cymbites, which is confined to the Birchi-obtusus zones. 



2 In Zittel-Eastman, vol. i, pp. 576-7, 1900. 



3 " On the Grouping of some Divisions of so-called 'Jurassic' Time": 

 Q.J.G.S., vol. liv, pp. 442-62 ; also in A Monograph of the Ammonites of the 

 " Inferior Oolite Series", Supplement, Pal. Soc, vols. 1898-1907, p. cxcviii. 



4 TraiU de PaUontologie, vol. ii, p. 673. 



