546 MOLLUSCA SUB-KINGDOM VI 
-carbonaceous coating; and Coalescentes (Fig. 1113) have the two thin plates 
A B 6 
a 
WA os aii 
ae at Ri ‘Goa 
. any ‘ ap 

eo 

at en i Y Hes 
c Fic. 1115. 
Vertical sections of aptychi belonging to A, Cellulosi (A. zonatus, Stopp.); B, Imbricati (A. profundus, Voltz) ; 
and C, Punctati (A. punctatus, Voltz). 3h (after Meneghini and Bornemann). 


fused along a median depression. This last is a phylogerontic condition of ° 
the aptychus occurring in Scaphites. 
Classificution.—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. dOrbigny, 
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 Mojsisovies’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, Douvillé, 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,! 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 sutlix cuompylus, 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 Tissotidae 
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. 

