34 L. F. Spath — Notes on Ammonites. 



modify, but to physical causes. To quote Diener, 1 " A flourishing 

 family like Lytoceratidae, which during the whole of the Cretaceous 

 period produced a number of irregular forms and which, itself, 

 persisted later than these irregular forms, cannot by any means be 

 considered degenerate." 



One of the most reduced types, with "goniatitic" suture, is 

 Flickia simplex, Pervinquiere, 2 which is a morphic equivalent of the 

 Triassic Lecanites. "Whether this is regarded as a local modification 

 of JSfeolohites or an independent benthonic dwarf development, its 

 Cenomanian age is of no significance; for the writer has seen 

 a specimen in the British Museum (Natural History) with a 

 similar entire suture-line (at a diameter of 12 mm.) from the 

 Caloceras bed of the Hettangian that looked like a Palaeozoic 

 Pronorites. The diminutive size of Fliclcia, of course, ■ suggests 

 unfavourable surroundings; but it appears that in the dwarf faunae 

 of Morade Ebro 3 and other localities the suture-line is little affected. 



It is conceivable that thickening of the shell may take place in 

 a series under local influences, i.e. increased lime-secretion, 

 shallowing of the sea, or alteration of the incoming sediment in 

 a more or less confined region. The simplification of the suture-line 

 of Metoicoceras * (Turonian Inoceramus facies) as compared with that 

 of the Cenomanian Acanthocerates may be due to such environ- 

 mental changes, affecting metabolism generally, and thus the 

 secretion of lime ; and this might also apply to the Ximmeridgian 

 Pictonm already mentioned, where the suture-line may be more 

 reduced than the ornament in one specimen, and the ornament more 

 than the suture in another. 



With regard to the simplification in individual Ammonites referred 

 to above, this follows on a continuous elaboration to often great 

 complexity, and is associated occasionally with approximation of the 

 last few septa, which association alone would account for the 

 simplification of the edge. Or, again, they may be thickened, like 

 the last septum of the recent Nautilus pompilius or certain Liassic 

 Nautili, and thus make up in the enlarging of the adhering surface 

 for what strength was lost in the simplification. No observations 

 seem to have been made on this point, however. 



It will be noted that in Psiloceras and other Ammonites the last 

 few suture-lines show what Swinnerton and Trueman in JDactylio- 

 ceras call "simpler and more turgid outlines of the folioles ", as 



1 Op. cit., 1912, p. 79. Freeh, " Neue Cephalopoden a. d. Buchensteiner, 

 Wengener, and Eaibler Schichten d. audi. Bakony " : Res. Wiss. Erf. 

 Balatonsees. Pal. Ann. z. Teil i d. Bd. i, p. 72 (quoted by Diener), expresses 

 similar views. 



2 The local restriction and numerical insignificance of this "goniatitic" 

 form compared with its normal contemporaries and the flourishing Scaphites 

 and Turrilites shows the incompleteness of the " cycle ". 



3 A. Wurm, " Beitr. Kenntn. Iberisch-Balearischen Triasprovinz " : Verh. 

 Naturhist.-mediz. Ver. Heidelberg, vol. xii, 4, 1913. This fauna is even 

 more reduced than that of St. Cassian, which it resembles. 



4 M. Leriche, " Sur la presence du genre Metoicoceras, Hyatt, dans la Craie 

 du Nord de la France, etc." : Ann. Soc. Geol. Nord, vol. xxxiv, pp. 120-4, 

 1905. 



