178 
THE LIAS AMMONITES. 
straight, elongated, conical, caraerated 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. Erom Silurian to Triassic 
strata. The OrtJioceratida now form a family composed of many genera that have been 
dismembered from Breynius' group. 
Genus. — Cameroceras, Conrad, 1842 ; Melia, Fischer, 1829. Shell straight, 
elongated, conical ; siphuncle lateral, sometimes large. Moulds of these large siphuncles 
were called Hyolites by Eichwald. L. Silurian to Trias. 
Genus. — Actinoceras, 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. — Ormoceras, Stokes, 1838. Siplmncular 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. — Hcronia, Bigsbg, 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 ; Drumraond Island, Lake Huron. Dr. Bigsby saw 
some specimens in the Limestone of Drummond Island six feet in length. 
Genus. — Endoceras, ^a//, 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 ; North America. 
5. Family Trochoceratid^, Wright, 1880. — Shells bent into a turbinated form. 
Genus. — Trochoceras, Barrande, 1847. Shell spiral, helicoidal. Position of 
siphuncle unknown. Lower Silurian, Bohemia. 
6. Family Gomphoceratid^, Pictet, 1855. — Shell fusiform, narrower before than in 
the middle, and with a contracted aperture. 
Genus. — Gomphoceras, /Sozt-'er^y, 1839. kvioc^^ks,, Fischer, 1844, Poterioceras, 
1844, M'Coy. Shell fusiform or globular, with a tapering apex. Aperture contracted 
in the middle. Siphuncle moniUform, subcentral. Silurian, Devonian, Carboniferous ; 
North America and Europe. 
Genus. — Oncoceras, Hall, 1847. Shell like Gomphoceras, but curved. Siphuncle 
external. Silurian ; North America. 
