242 



THE LIAS AMMONITES. 



Genus Trachyceras, Laube. — Body-chamber short, from one half to two thirds 

 of a whorl in length. The sculpture interrupted on the ventral surface (fig. 140.) In 



Fig. 139. Fig. 140. 



Trachyceras Aon, Miinst. 



some species there is a deep median furrow, at which the ribs with their tubercles end. 

 The mouth-border has a short ventral process. All the species are Triassic. Ex. 

 Tracliyceras Aon, Miinst. (figs. 139, 140). Tracli. binodosum, Hau., Track. Attila, Mojs. 



Genus Choristoceras, Hauer. — This genus is nearly allied to the preceding. The. 

 body-chamber is short; the lobes are very slightly incised. The inner whorls have 

 their sculpture interrupted on the ventral surface, whilst on the last whorl it extends 

 uninterruptedly across the abdomen. The structure of the lobes shows a persistent 

 relation to an older type, whilst in the sculpture on the ribs there is an evident 

 inclination towards the Trachyceras type. All the species belong to the Trias formation, 

 Ex. Choristoceras decoratum, Hauer, Chor. noricum, Mojs., Chor. nasturtium, Dittm. 



Getms Rhabdoceras, Hauer. — Staff-shaped and tubular, with expanded mouth, and 

 with a transverse ring-like sculpture and simple bent lobes ; the genus is very little 

 known, and probably connected with Choristoceras, to which it stands very near. B. 

 Suessi, Hauer, 



Genus Cochloceras, Hauer. — The whorls are screw-shaped, with continuous ribs 

 and simple bent lobes. This form is also near to Choristoceras ; it is found in the Trias 

 beds at Zamblach and Salzkammergut. Cochl. Fischeri, Hau. 



III. Family. — Lttoceratid^, Neumayr. 



This family includes several groups which differ much from each other as regards their 

 external form, but which nevertheless appear to have a close relationship in their 



