194 MANUAL OF THE MOLLUSCA. 



Shell, like a curved gomphoceras ; siphuncle external. 

 Distribution, 3 species. Silurian, New York. 



Phragmocekas, Broderip. 



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



Type, P. ventricosum (Steininger species), PI. II., Fig. 15. 



Shell curved, laterally compressed ; aperture contracted in the 

 middle ; siphuncle, ventral, radiated. Example, P. callistoma, 

 Bar., Fig. 48. 



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

 Germany. 



Cyrtoceras, Goldf., 1832. 



Etymology, curtos, curved, ceras, horn. 



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

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

 Gyroceras, D'Orbigny. 



Example, 0. bybridum, Yolborthi, and Beaumonti (Barrande). 



Shell curved ; siphuncle small, internal, or sub-central. 



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

 America and Europe. 



Fig. 59.» 



Gyroceras, Meyer, 1829. 

 Etymology, gyros, a circle, and ceras. 

 Synonym, Nautiloceras, D'Orbigny. 



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

 Eifel. 



* Fig. 59. Gyroceras Goldfussii. {= omatiftn Goldf.). 5, siphuncle of G. depressunit 

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



