Ammonites of the Mediterranean and Juvavian Trias. 461 



the genus Arcestes, Suess, comprises the groups of Extra-labiati, 

 Sub-labiati, Bi-carinati, Coloni, Intus-labiati, Galeati, and Sub- 

 umbilicati ; all of them characterized by more or less modified 

 body-chambers of the full-grown individuals and by a contraction 

 of the umbilicus, frequently occluded by a callosity. 



Sphingites, Mojs. — This genus comprises the group of Co-angustati, 

 characterized by a widely open umbilicus, pi-ominent ridges, and 

 strictures in the shell of the whorls, including the inhabited chamber, 

 and coarse wrinkled striations. Cladiscites, Mojs. — The Tomati and 

 Midtilobati bear a number of characters different from those of the 

 typical Arcestes. The constantly closed whorls, of nearly quadi'an- 

 gular transverse section, show neither internal nor external ridges 

 and keep their form even in the last whorl of full-grown individuals. 

 Their lobes offer a peculiar structure. The projection of the pre- 

 ceding whorl coincides with the first auxiliary lobe, not, as in all 

 other Arcestidce, with the second lateral lobe. This is an approxi- 

 mation to the distribution of the lobes of the Pinacoceratidce, and 

 becomes still more conspicuous in Cladiscites sub-tomatus by the 

 deepening of the second lateral lobe. Prof. Quenstedt was the first 

 who noticed the peculiar structure of the anti-siphonal lobe with its 

 two many-jointed branches. 



Joannites, Mojs. — Like the Tomati, the Cymbiformes are to be generi- 

 cally separated, as they agree in every respect with Arcestes except 

 in the form of their lobes, which is the same as in the genus Cladiscites. 

 They are characterized by their arcuate lobe-line. 



Didymifes, Mojs. 



Lobites, Mojs.= Clydonites, Laube,= Coroceras, Hyatt. 



Amaltheid^;. 



Ptycliites, Mojs. 



Amaltlieus, Montf. — Triassic forms, standing next to the group of 

 Fissi-lobati. The Amalthei comprise a number of evidently distinct 

 groups, which may be generically separated. 



PlNACOCERATIDiE. 



Pinacoceras, Mojs. 



MegapliyUites, Mojs. — The group of Megaphylli, Beyr. (Type : 

 Ammonites Tarbas), differ from Pinacoceras in the form of their 

 lobes. 



Sageceras, Mojs. 



Carnites, Moys. — Comprises Carnites floridas, Wulf., Cam. rari- 

 striatus, Hauer, and a nondescript species from the Muschelkalk. Very 

 probably this genus is to be connected with Ceratites Redenstrozmi, 

 Keys., or with a form nearly allied to it. The form of the lobes 

 distinguishes Carnites from Pinacoceras. 



Norites, Mojs. — The Triassic species are — Norites Caprilensis, 

 Mojs., and Nor. Gondola, Mojs. Shell similar to Sageceras. Kugose 

 stratum linear. One adventitious saddle of less height than the first 

 primary saddle. Saddles narrow, high, rounded above. Lobes with 

 few indentures, first chief lobe divided by a large indenture. More 

 ancient forms from the sandstones of Artinsk, described by de 



