MODERN CLASSIFICATION. 



231 



II. Aptychus divided (bivalved) calcareous, 



1. Aptychus, externally furrowed. 



Apfychus thin, body-chamber short, mouth-border 

 falciform, with pointed ventral process 



Aptychus thick, body-chamber short, mouth- 

 border falciform, appendage rounded ventral. 



Body-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. Body- 

 chamber long, mouth-border simple, or furnished 

 with bands or auricles. 



Body-chamber long, aperture narrowed by a 

 furrow, simple, or provided with auricles. 



Body-chamber short, aperture simple, or furnished 

 with auricles. 



3. Aptychus thick, smooth, and punctated externally. 



Body-chamber long, umbilicus wide ; shell with 

 furrows, aperture with a ventral nasiform appen- 

 dage. 



Body-chamber short, mouth-border in general 

 simple. 



Harpoceras, Waagen. 



Jurassic. 

 Oppelia, 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 = the uppermost 

 Jurassic strata. 

 AspiDOCERAS, Zittel. 



Jurassic and Cetaceous. 



Since the above scheme was proposed many important additions have been made to 

 the number of genera. Dr. E. Mojsisovics has revised the family Arcestidjs, and 

 grouped therein several new generic forms discovered by him in the Zlambach und 

 Hallstatter-strata, and which are figured in detail in his splendid Monograph.^ 



Professor M. Neumayr, of Vienna, has proposed the genera Olcostephayius, lioplites, 

 Acanthoceras, and Stoliczkaia for certain forms which have been detached from other 

 genera owing to the discovery of new characters in these special forms, and Dr. Waagen 

 has proposed the genus Peltoceras for certain forms which he has described in his great 

 work on the Jurassic Cephalopoda of Kutch in India. 



As new discoveries are made in the intricate structure of these polythalamous 

 shells many errors will be corrected, omissions supplied, and new genera erected for the 

 reception of the revised types of this wonderful assemblage of Cephalopoda which have 

 been collected from the Secondary (Mesozoic) rocks of the Continent of Europe, and from 

 beds of the same age in Asia. The Cephalopoda of the Cretaceous Rocks of Southern 

 India have been admirably figured and described : Belemnitidce and Nautilidce, by Henry 



1 'Das Gebirge um Hallstatt,' Wien, 1875. 



