194 MAIfTJAL OF THE MOLLTJSCA. 



Shell, like a curyed gomphoceras ; sipliiincle external. 

 Distribution, 3 species. Silurian, New York. 



Phragmocebas, Broderip. 



Etymology, phragmos, a partition, and ceras, a horn. 



Type, P. yentricosum (Steininger species), PL II., Pig. 15. 



Shell curyed, laterally compressed ; aperture contracted in the 

 middle ; siphunde, yentral, radiated. Example, P. callistoma, 

 Bar., Pig. 48. 



Distribution, 15 species. Lower Silurian — Carb. ; Brit., 

 Germany. 



Cyhtoceeas, Goldf., 1832. 



Etymology, curtos, curyed, ceras, horn. 



Synonyms, Campulites, Desh., 1832 (including gyroceras). 

 Aploceras, D'Orbigny. Campyloceras and trigonoceras, McCoy. 

 Gyroceras, D'Orbigny. 



Example, 0. hybridum, Yolborthi, andBeaumonti (Barrande). 



Shell curyed ; siphunde small, internal, or sub-central. 



Fossil, 84 species. Lower Silurian — Carb. ; North and South 

 America and Europe. 



Pig. 59.* 



Gtroceeas, Meyer, 1829. 

 Etymology, gyros, a circle, and ceras. 

 Synonym, Nautiloceras, D'Orbigny. 



Example, G. eifeliense, D'Arch. (PI. II., Pig. 13). Devonian; 

 Eifel. 



* Fig. 59. Gyroceras Goldf ussii. {— omatifm Groldf.). b, siphimcle of G. depressum, 

 Goldf. sp. Devonian. Eifel. From MM. D'Archiac and Vemeuil. 



