CEPHALOPODA. 



91 



Cyrtoceras, Goldf, 1833. 

 Etym., curtos, curved, ceras, horn. 



Spi., Carupiilites, Desh. 1832 (including gyroceras). Aploccra.s, D'Orb 

 Campyloceras and trigonoccras, McCoy. 



Ex., C. hybridum, volborthi and beaumonti (Ban-ande). 

 Shell, cun'ed ; sii[)kuncle smaU, internal, or sub-central. 

 jyistr., 36 sp, L. Silurian, Carb— N. America, and Europe. 



Fig. 52.* 



Gyroceras, Meyer, 1829. 

 Etym., gyros, a circle, and ceras. 

 Hyn., Nautiloceras, D'Orb. 



Ex., G. eifeliense, D'Arch., pi. XL, fig. 13. Devonian, Eifel. 

 Shell, nautiloid ; wMrls separate ; siphuncle excentric, radiated. 

 Fossil, 17 sp. U. Silui-ian — Trias ? N. America, and Europe. 



AscocERAS, Barrande, 1848.t 

 Etym., ascos, a leather bottle. 

 Shell, bent upon itself, like ptychoceras. 

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



FAMILY III. AMM0XITIDJ5. 



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

 closed by an operculum ; sutures angulated, or lobed and foliated ; siphuncle 

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



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

 nautilus. It consists of an external porceUanousij: layer, formed by the collar 



* Fig. 52. Gyroceras goldf ussii {= ornatum Goldf). b. Siphuncle of G. depresaum, 

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



t In Haidinger's Berichte. 



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

 detected a punctate structure in one species. 



