546 MOLLtlSCA SUB-KINGDOM vi 



carbonaceous coating; and Coalescentes (Fig. 1113) have the two thin plates 



c Fie*. 1115. 



Vertical sections of aptychi belonging to A, Cellulosi (A. zonatus, Stopp.) ; B, Imbricati (A. profundus, Yoltz) ; 

 and (.', Punctati (A. punctatus, Voltz). 3/j (after Meneghini and Bornemann). 



fused along a median depression. This last is a phylogerontic condition of 

 the aptychus occurring in Scaphites. 



Classification. Leopold von Buch prepared the way for a general classifica- 

 tion of the Ammonoidea by pointing out three grand divisions which he called 

 " genera." These were the Palaeozoic Goniatites, Ceratites, from the Trias and 

 Cretaceous, and Ammonites, from the Jura and Cretaceous, von Buch's chief 

 distinctions were based on the outlines of the lobes and saddles, and were as 

 natural and well-founded as the knowledge of the time permitted. d'Orbigny, 

 Quenstedt, Sandberger, and Barrande greatly increased our knowledge of 

 structure and variation, and defined a number of new genera. 



The next marked epoch dates from the publication of Mojsisovics's great 

 works on the Trias, which made known a fauna as rich and complex as that 

 of the Jura. Suess, Neumayr, Branco, Waagen, Buckman, Grossouvre, Haug, 

 Diener, Douville", Kilian, Zittel, Karpinsky, the present writer, and others 

 made advances of essential importance along different lines. All of these 

 authors attempted to trace phylogenetic histories which of necessity crossed 

 the lines of the older classifications at right angles, and sometimes bridged 

 over the divisions 'of geologic time. 



All classifications have necessarily been based upon sutural peculiarities. 

 That which is put forward below differs mainly in that it attempts to divide 

 Ammonoids into a number of sub-orders, named with reference to peculiarities 

 of the saddles, 1 and lays special stress upon the phylogenetic significance of 

 the dorsal and internal sutures, especially the antisiphonal lobe. Although 

 some extensive changes are proposed, the system is in reality only a modifica- 

 tion of the older schemes, as will be seen from an inspection of the following 

 table. The latter is intended to facilitate comparisons between the primary 

 divisions formerly recognised and the new sub-orders, which are assembled by 

 means of brackets on the left into four corresponding groups. 



1 The suffix campylus, signifying curve, in the names of the sub-orders, is used wholly with 

 reference to the saddle inflections as they appear in the typical forms of each group. The term 

 "Pseudoceratites," as used above, is a descriptive expression for the Placenticeratida and Tissotid/n' 

 of the Cretaceous, which are morphic equivalents of some Triassic genera of the Discocampyli as 

 regards both sutures and shell form. Their origin is traceable, however, to different groups of the 

 Pachycampyli, a sub-order which appears to have been initiated in the Jura along with the Lepto- 

 campyli. It is therefore improbable that the Pseudoceratites were directly connected with the 

 Triassic Discocampyli. 



