32 L. F. Spath — Notes on Ammonites. 



of their margins. With regard to Pictonice, Tornquist 1 stated : " We 

 get the impression that they are Ammonites that have resulted from 

 different groups of normal Ammonites, through general degeneration 

 effecting them under local influences during Kimmeridgian times." 

 It must be repeated here that development or loss of strengthening 

 ornament on the shell would affect the suture-line as much as change 

 of whorl-shape. For e.g. in Pictonia cymadoce the ornament may be 

 more "reduced" than the suture-line in one specimen, and in 

 another the suture-line more than the ornament. 2 



Adaptation to a ISTautiloid, or less exclusively swimming mode of 

 life, 3 might have taken place in Frechiella, which is also often one- 

 sided and which shows the modification of its ancestral ITildoceras 

 suture-line in its ontogeny. And the oxycones of Hudlestonia and 

 Stanfenia were better adapted to an actively swimming existence 

 than their Grammoceratan and Ludwigian ancestors. With Benz 

 and J. von Pia i the writer would be inclined to favour the theory of 

 adaptation, therefore, even if the special mode of adaptation be not 

 quite clear in some cases, rather than speak of decline of vitality or 

 phylogenetic degeneration. 



Wholesale Phyletic " Catagenesis". 

 This applies, of course, also to the modification of the suture-line 

 in the Cretaceous Pseudoceratites, which, however, is on a different 

 scale, and which has been explained as a phenomenon coincident 

 with the approaching end of the whole race of Ammonites. Walther 5 

 had stated: "Ammonites, after dominating the seas through three 

 long periods and hearing, their end, show in all groups such clear 

 symptoms of abnormal growth, such evident signs of senile 

 degeneration, that their extinction through a kind of senile decay 

 seems to us inevitable." As far as it affected the suture-line, this 

 "degeneration" produced "forms which remind one of Triassic 

 Ceratites and even of certain Palaeozoic Goniatites ". 6 Indeed, 

 Neolohites Vibrayanus (d'Orbigny) and Metatissotia Eivaldi (v. Buch) 

 e.g. had been put into the genus Ceratites by d'Orbigny and even 

 into Goniatites by Pictet. Just as in the modification of the shell, 

 only certain lineages were affected, however, and these differently 

 and at different horizons. But this going back, as it were, along the 

 line followed in the evolution of the group from Goniatites through 

 Ceratites to Ammonites, however incomplete, fitted into the 

 representation of Ammonite phylogeny as a series of cycles "which 



1 Op. cit., p. 42. 



2 Ibid., p. 39. 



3 Diener (" Lebensweise u. Verbreitung d. Ammoniten " : N. Jahrb. 

 Miner., etc., ii, p. 69, 1912) says that Nautilus lives chiefly crawling, but can 

 swim well and quickly, and has also been found attached to the bottom, which 

 " shows that its present mode of life is little stable yet ". Diener, therefore, 

 does not agree with Dollo (" Les Cephalop. adaptes a la vie nect. second, et 

 k la vie benthique tertiaire " : Zool. Jb. Spengel. Festschr., Suppl., xv, 1, 

 p. Ill, 1912), who ascribes a primarily benthonic mode of life to Nautilus, the 

 " type of the ancient Cephalopod with functional, external shell ". 



4 N. Jahrb. Miner., etc., ii, p. 169, 1913 (in review of Renz). 



5 Geschichte der Erde und des Lebens, 1908, p. 451. 



6 Haug, TraiU de Giologie, vol. ii, fasc. ii, p. 1166, 1908-11. 



