185 
the dwelling-chamber of the shell, its mouth-border and lateral 
processes all complete, and in these specimens the relative 
position of the Aptychi agrees with what I have stated. 
Having described in detail the five characters upon which 
Paleontologists have based the diagnosis of genera, I now 
proceed to give the classification proposed by Dr. WAAGEN; | 
as it exhibits, in an analytical form, the results of modern 
investigations on the different groups of the AmmonrTIDz. 
The difficulty of finding the Aptychus in sité in the shells to 
which it belongs will long render this important anatomical 
character of little practical value as a factor in the diagnosis 
of the different groups, and for this reason it has not been 
employed by Dr. E. Mosstsovies or by Professor Neumayer in 
the classifications given by them. 
The following classification of the new Ammonite genera 
was proposed by Dr. W. Waacen,* and a like grouping has 
since been published by M. HE. Favrz.t 
GENERA OF AMMONITES. 
A. Aptychus, ABSENT. 
Dwelling-chamber short; appendage ventral. PHYLLOCERAS, Suess. 
Triassic and Cretaceous. 
Chamber short, appendage dorsal. LyTOCERAS, Suess. 
Trias., Juras., Cretaceous. 
Chamber very long, one and a half to two ARcESTEs, Suess. 
whorls, mouth-border dissimilar. Triassic. 
Chamber short, mouth-border falciform, ap- Tracuycrras, Laube. 
pendage ventral, sculpture Argonautiform. Triassic. 
B. Aptychus PRESENT. 
I Aptychus undivided. 
1 Horny (Anaptychus )— 
Chamber long, one to one and a half ‘whorls, ARIETITES, Waagen. 
mouth-border with pointed ventral ap- Triassic and Liassic. 
pendage. 
ede ase 
® “Ueber die Ansatzstelle der Haftmuskeln beim Nautilus und den Ammo- 
niden. Palzontographica,”’ Band xvii, 5, p. 197. 1867—1870. 
+ “Sur la Classification des Ammonites,” M. E. Favre, “ Bulletin de Soe. 
Geol. de France, 3e serie, tom i. p. 353. 1873. 
P 
