186 
Chamber from two thirds to an entire 
whorl, mouth-border with rounded ven- 
tral appendage. 
Chamber short, one half to two thirds of a 
whorl, mouth-border with long ventral 
appendage. 
2 Calcareous,—Aptychus Numida, Coquand. 
Shell unknown (Sidetes?) Cretaceous. 
II Aptychus divided (bivalved) calcareous. 
1 Aptychus externally furrowed. 
Aptychus thin, chamber short, mouth-border 
falciform, with pointed ventral process. 
Aptychus thick, chamber short, mouth-bor- 
der falciform, appendage rounded ventral. 
Chamber short, mouth-border with a groove 
or enlargement near the aperture, mouth- 
border with lateral auricles, and rounded 
ventral appendage. 
2 Aptychus thin, granulated externally. 
Chamber long, mouth-border simple, or 
furnished with bands or auricles. 
Chamber long, aperture narrowed by a 
furrow, simple, or provided with auricles. 
Chamber short, aperture simple, or fur- 
nished with auricles. 
3 Aptychus thick, smooth, and punctated 
externally. 
Chamber long, umbilicus wide ; shell with 
furrows, aperture with a ventral nasi- 
form appendage. 
Chamber short, mouth-border in general 
simple. 
AEGOCERAS, Waagen. 
Triassic and Liassic. 
Amattugvs, Montfort. 
Trias., Juras., Cretaceous. 
Harpoceras, Waagen. 
Jurassic. 
OppEtia, Waagen, 
Jurassic, Cretaceous. 
HAPLOCERAS, Zittel, 
Jurassic and Cretaceous. 
STEPHANOCERAS, Waagen, 
Jurassic and Cretaceous. 
PERISPHINCTES, Waagen, 
Jurassic and Cretaceous. 
Cosmoceras, Waagen. 
Jurassic and Cretaceous. 
SIMOCERAS, Zittel, 
Tithonic. 
ASPIDOCERAS, Zittel. 
Jurassic and Cretaceous. 
Since the above scheme was proposed many important 
additions have been made to the number of genera. Dr. E. 
Moasstsovics has revised the family Arcestide, and grouped therein 
several new generic forms he had discovered in the Zlambach 
und Hallstatter-Schichten, and which he has figured in detail 
in his splendid Monograph.* 
Professor M. Nrumayr, of Vienna, has proposed the genera 
Olcostephanus, Hoplites, Acanthoceras and Stoliczkaia for certain 
* “Das Gebirge um Hallstadt,” Wien, 1875. 
