CEPHAIOPODA. 



193 



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

 cayity, formed by the approximation of tbe lateral angles. 



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

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

 Bigsby in 1824 (Geol. Trs. I., PI. 30, f. 6), and which haye been 

 correctly referred to the orthocerata by Quenstedt. 

 GoMPHOCERAS, J. Sby. 1839. 



Etymology, gomjplios, a club ; and ceras, a horn. 



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



Type, G. pvrifonne, Sby., Fig. 5S, and G. Bohemicum, Pax. 

 Fig. 47. 



e o.c 



Fig. 57. Endoccras.* Fig. 58. Coniphoceras.\ 



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

 contracted in the middle ; siphuncle moniliform, sub-central. 



Disirihution, 27 species. Lower Siluiian — Garb. North 

 America, Europe, Brit. Barrande figures 70 species in Vol. II. 

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

 to be new. 



Oncoceeas, Hall. 



Etymology, oncos, a protuberance. 



Tyjie, 0. constrictum, Hall. Trenton limestone. 



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

 tec, diaphragms (" embrj'o- tubes " of Hall). 



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

 (From Murchison's Siliurian Syst. reduced f .) s, beaded siphuncle. 



