CrEPHALOPODA. 



193 



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

 cavity, formed by the approximation of the lateral angles. 



Disoosorus [conoideus) Hall, 1852. Pal. New York. This 

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

 Bigsby in 1824 (Geol. Trs. I., PL 30, f. 6), andwMch have been 

 correctly referred to the orthocerata by Quenstedt. 

 GoMPHOCEEAS, J. Sby. 1839. 



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



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



Tyoe, G. pyriforme, Sby., Pig. 5S, and G. Bohemicum, Bar. 

 Fig. 47. 



Fig. 57. Endoceras.* Fig. 58. Gomphoceras.^ 



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

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



Distribution, 27 species. Lower Silurian — Garb. North 

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

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

 to be new. 



Oncoceeas, HaU. 



Etymology, oncos, a protuberance. 



Type, 0. constrictum, Hall. Trenton limestone. 



* Fig. 57. Diagram of an endoceras (after Hall), a, shell-wall; 6, wall of siphuncle * 

 ecc, diaphragms ("embryo-tubes" of Hall). 



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

 JFrom Murchison's Silurian Syst. reduced ^.) s, beaded siphuncle. 



