178 THE LIAS AMMONITES. 



straight, elongated, conical, canierated in the greatest portion of its length. Septa trans- 

 verse, simple, concave forwards. Siphuncle complicated, central or subcentral. Aperture 

 simple, circular, sometimes banded. A very extensive genus ; some of the species 

 attained large dimensions ; and, from fragments, it is estimated that 0. giganteum 

 might have been six feet long and above a foot in diameter, from Silurian to Triassic 

 strata. The Orthoceratidce now form a family composed of many genera that have been 

 dismembered from Breynius' group. 



Genus. — Camerocebas, Conrad, 1842 ; Melia, Fischer, 1829. Shell straight, 

 elongated, conical ; siphuncle lateral, sometimes large. Moulds of these large siphuncles 

 vpere called Hyolites by Eichwald. L. Silurian to Trias. 



Genus. — Actinocebas, Bronn, 1835. Siphuncle very large, inflated between the 

 chambers, and connected with a central tube by numerous radiating plates. Silurian, 

 Devonian, Carboniferous ; North America, Baltic, and British Islands. 



Genus. — Ormocebas, StoJces, 1838. Siphuncular beads constricted in the middle, 

 making the septa appear as if united to the centre of each. They are essentially the 

 same as Actinoceras. Lower Silurian ; North America. 



Genus. — Hdbonia, Bigshy, 1824. Shell very thin. Siphuncle very large and 

 central, the upper part of each joint inflated, connected with a small central tube by 

 radiating plates. Lower Silurian ; Drummond Island, Lake Huron. Dr. Bigsby saw 

 some specimens in the Limestone of Drummond Island six feet in length. 



Genus. — Endocebas, ^«^/, 1847. Shell straight, elongated, conical. Siphuncle large 

 and marginal, thickened internally by repeated layers of shell, or partitioned off by a series 

 of funnel-shaped diaphragms. Lower Silurian j North America. 



5. Family Trochoceratid^, Wright, 1880. — Shells bent into a turbinated form. 



Genus. — Tbochocebas, Barrande, 1847. Shell spiral, helicoidal. Position of 

 siphuncle unknown. Lower Silurian, Bohemia. 



6. Family Gomphocebatidjs, Pictet, 1853. — Shell fusiform, narrower before than in 

 the middle, and with a contracted aperture. 



Genus. — Gomphocebas, /Soziz-er^y, 1839. k?ioc-&-&k9,, Fischer, 1844, Potebiocebas, 

 1844, M^Coy. Shell fusiform or globular, with a tapering apex. Aperture contracted 

 in the middle. Siphuncle moniliform, subcentral. Silurian, Devonian, Carboniferous ; 

 North America and Europe. 



Genus. — Oncocebas, Hall, 1847. Shell like Gonvphoceras, but curved. Siphuncle 

 external. Silurian ; North America. 



