90 



MANL'AL OF THE 310LLUSCA. 



ty>?.. Apioceras (Fisclier). Poterioceras (McCoy). 



Type, G. pyriforme, Sby., fig. 51, and G. Bohemicum, Bar. fig. 40. 



!> eoc 



Fig. 50. Endoceras.* 



Fig. 51. Gomphoceras.i 



Shell, fusiform or globular, with a tapering apex ; aperture contracted 

 the middle ; siphuncle moniliforni, sub-central. 



Di$tr. t 10 sp. Silurian Garb ; N. America, Europe. 



ONCOCERAS, Hall. 



Eti/m. y oncos, a protuberance. 

 Type, O. constrictum, Hall. Trenton limestone. 

 Shell, like a curved goinphoceras ; siphuncle external. 

 Distr., 3 sp. Silurian, New York. 



PHKAGMOCEEAS, Broderip. 



Etym., phragmos?* partition, and ceras, a horn. 

 Type, P. ventricosum (Steininger sp.), pi. II., fig. 15. 

 Shell curved, laterally compressed : aperture contracted in the mid 

 sipJi uncle, ventral, radiated. Ex., P. callistoma, Bar., fig. 41. 

 Distr., 8 sp. U. Silurian Devonian, Brit., Germany. 



* Fig. 50. Diagram of an endoceras (after Hall), a, shell-wall 6. Wall of s 

 huncle. c c c. Diaphragms (" embryo-tubes " of Hall). 



t Fig. 51. Gomphoceras pyriforme. L. Ludlow rock, Mochtre hill, Herefords] 

 (from Murch, Silur, syst., reduced ^). *. Beaded siphuncle. 



