L. F. Spath — Notes on Ammonites. 31 



adaptations to a benthonic existence, the suture-line is not affected. 

 But in such aberrant types as Cochlocerax, Ithabdocerm, and 

 Chorifttoeerax, where the reduction of the septal edges to great 

 simplicity is accompanied by modifications of the coiling, the 

 adaptation to a different mode of life can scarcely be doubted. 

 Professor J. P. Smith 1 calls these "reversionary" types; but if the 

 reduction of the suture-line and uncoiling were reversions to a 

 primitive type, they should be preservative. The writer would also 

 look upon (Ecoptychvw Chrittoli, Beaudouin, sp., Popanites 

 patturatensis, Greppin, sp., mid similar forms as aberrant, benthonic 

 types. 



"pliylogerontic " suture-lines. correlation of snture-line and 



Ornament. 



With regard to the "reduction'' of the suture-line, distinction has to 

 be made between such simplification as is shown in many individual 

 Ammonites, where the last few septa may be simpler and be 

 associated with an (equally sporadical) approximation. This is 

 a growth-phenomenon of the individual. The formation of septa 

 probably ceased when maturity was reached and the character does 

 not become " phylogerontic " ; for the stock may continue to 

 elaborate its suture-line. Or, again, in the broad stream of develop- 

 ment of a whole family, one branch, under local influences or owing 

 to a tendency to diversity, may modify or simplify its suture-line. 

 It is clear that if whorl-shape and suture-line (and of course also the 

 other characters of the shell) are as closely interconnected as the 

 writer believes, a form like Hudlestonia must adapt the suture-line 

 of its probable ancestor Phlyseogrammoceras to an oxynote shell, with 

 wide lateral area, according to the general rules mentioned above. 



Similar modification is shown in Staufenia and Clydoniceras." 1 

 The latter, a local development 3 of the Bathonian Oppelice, does not 

 so much "reduce" its suture-line as, rather, take on a specialized 

 type that resembles certain " Pseudoceratites ", with an increased 

 number of elements, but less frilling. It is to be noted that the 

 families themselves (Ludwiginse and Oppelidse) are not affected. 

 In Proplanulites and Pictonia* the reduction is shown in the 

 shortening of the saddles and lobes and the decreased complication 



1 In Zittel-Eastman, Text-book of Pal., 2nd ed., vol. i, p. 673, 1913. 



2 Menzel, Zeitschr. Deutsch. Geol. Ges., vol. liv, p. 90, 1902. 



3 Blake (in Great Oolite Mollusca, Mon. Pal. Soc. vol.), from the occurrence 

 of this genus in the southern part only of the Cornbrash outcrop in England, 

 concluded that it was dependent on the presence of the Great Oolite Series 

 below, of whose fauna it was a relic. Compared with the almost universal 

 distribution of the genus Macrocephalites , this restriction of Clydoniceras is 

 interesting and shows that, like many modern marine organisms, certain 

 Ammonite genera were undoubtedly strictly limited in their horizontal 

 distribution. In aberrant or benthonic types, of course, like the Oxynoticeras 

 derivative " JEgoceras " Slatteri, Wright, or Nipponites, the local restriction 

 might be expected, more than in active swimmers. 



4 Tornquist, "Proplanuliten a. d. Westeuropaischen Jura " : Zeit. Deutsch. 

 Geol. Ges., vol. xlvi, 1894; also "Die degenerierten Perisphinctiden d. 

 Kimmeridge v. Le Havre " : Abb. Schweiz. Pal. Ges., vol. xxiii, 1896. 



