CErnALoroDA. 



193 



have resembled Gonioceras, and tlie external tube to be a simple 

 ca-sdty, formed by the approximatioii of the lateral angles. 



Discosorus {conoideus) Hall, 1852. Pal. New York. This 

 fossil appears to be a siphuncle similar to those figured by Dr. 

 Bigsbyin 1824 (Geol. Trs. I., PI. 30, f. 6), and which have been 

 correctly refeired to the orthocerata by Quenstedt. 

 GoMPHOCERAS, J. Sby. 1839. 



EiymoJocy, gon,phos, a club ; and ceras, a horn. 



Synonyms, Apioceras (Fischer). Poterioceras (McCoy). 



Tyne^ G. pyriforme, Sby., Eig. 5S, and G. Bohemicum, Bar. 

 Fig. 47. 



6 eoc 



Fig. 67. Endoceras.* Fig. 58. Gomphoceras.^ 



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

 contracted in the middle ; siphuncle monih'form, sub-central. 



Distribution, 27 species. Lower Silurian — Garb. North 

 A-merica, Europe, Brit. Barrande figures 70 species in Yol. II. 

 of his " Systeme Silurien," 1865, nearly all of which are believed 

 to be new. 



Oncoceeas, HaU. 



Etymology, oncos, a protuberance. 



Tyj>e, 0. constrictum, HaU. Trenton limestone. 



* Fig. 57. Diagram of an endoceras (after Hall), a, shell-wall; b, wall of siphuncle ' 

 cc c, diaphragms (" embrj-o-tubes " of Hall). 



t Fig. 58. Gomphoceras pyriforme. L. Ludlow rock, Mocktree Hill, Herefordshire. 

 iFrom Murchison's Siliuian Syst. reduced ^.) s, beaded siphuncle. 



