MODERN CLASSIFICATION. 



221 



of the Ammonite shell/ " Die Zusammensetzung der spiralen Schale," The reform so well 

 inaugurated by Professor Suess was ably followed up by Dr. W. Waagen," who directed 

 attention to the importance of the study of the Antychis and Anaplychus, and the presence 

 or absence of this body in the Ammonite shell. The observations made by Waagen on 

 the Aptychus\it described and applied in the diagnosis of the genera proposed for several 

 Jurassic species. In the following figure the Aptychus carinaim (fig. 98) is seen apart 

 from the shell. In figure 97 it is seen lying in the body-chamber of an Ammonite, 

 and in figure 99 the Aptychus is vertical, as if closing the aperture of the shell. 



The following organic features are considered as elements of primary importance in 

 studying the Ammonite shell, and their combination constitutes characters for the 

 diagnosis of the generic groups. 



Firstly. — The structure of the lobes and their suture-line have been fully studied by 



Fig. 100. — Disposition of the lobes 

 (d, l, l', a) in Amal. margari- 

 taius, Montf. 



Fig. 101. — Disposition of the lobes 

 (d, l, h', a) in Phylloceras hetero- 

 phyllum. 



Fig. 102. — Disposition of the lobes 

 (d, l, l', a) in Phyll. heterophyl- 

 lum. Sow. 



1 'Ueber Ammoniten,' 2 Abth., Sitxungsber. der Mathemat. Classe der Wiener Akademie Band 

 61, Abth. 1, 1870. 



2 " Die Formenreihe des Ammonites subradiatus ," Benecke'a ' Geogn.-Palfeont. Beitrage,' Bd. ii, 1869. 



