CEPHALOPODA. 



I 



Cyetoceras, Goldf. 1833. 

 Etym., cur to s, ciu'\'ed, ceras, horn. 



Si/n., Campulites, Desh. 1832 (including gyroceras). Aploceras, D'Orb. 

 Campyloceras and trigonoceras, McCoy. 



Ex., C. hybridum, volborthi and beaumonti (Barrande). 

 Shell, curved ; sij)huncle small, internal, or sub-central. 

 Distr., 36 sp. L, SUui'iau, Carb — N. America, and Europe. 



Pig. 52.* 



Gyroceras, Meyer, 1829. 

 Eti/m., gyros, a circle, and ceras, 

 Syn., Nautiloceras, D'Orb. 



Ex., G. eifeHense, D'Ai-ch., pi. II., fig. 13. Devonian, Eifel. 

 Shell, nautiloid ; whiiis separate ; sipbuncle excentric, radiated. 

 Fossil, 17 sp. U. Silurian — Trias ? N. America, and Em'ope. 



AscocERAS, Barrande, 1848.t 

 Etym., ascos, a leather bottle. 

 SJiell, bent upon itself, like ptycJioceras. 

 Distr., 7 sp. U. Silurian, Bohemia. 



FAMILY III. Ammonitid^. 



Shell. Body-chamber elongated; aperture guarded by processes, and 

 dosed by an operculum ; sutures angulated, or lobed and foliated ; sipkuncle 

 external (dorsal, as regai-ds the sheU). 



The shell of the ammonitida has essentially the same structure with the 

 nautilus. It consists of an external porceUanous^ layer, foimed by the collar 



* Fig. 52. Gyroceras goldfussii (= ornatum Goldf). b. Siphuncle of G. depressum, 

 Goldf. sp. Devonian. Eifel. From M.M. D'Archiac and Verneuil. 



t In Haidinger's Berichte. 



I Its microscopic structure has not been satisfactorily examined ; Prof. Forbes 

 detected a punctate structui'e in one species. 



