MODERN CLASSIFICATION. 
231 
II. Apti/chm divided (bivalved) calcareous. 
1. Aptychis, externally furrowed, 
Aijtyckus 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. 
Harpocebas, 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. 
ASPIDOCBRAS, 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 Arcestid^, 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 Olcostephanus, IlopUtes, 
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 : Belemnitidts and Nautilida, by Henry 
'Das Gebirge um Hallstatt,' Wien, 18/5. 
