THE CEPHALOPODA. 
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40. Hercoceras, Barrande, 1865. 
Turns of the shell at first in contact, slightly overlapping, afterwards spirally 
divergent ; siphuncle marginal on outer side, edge of exterior chamber contracted and 
compressed transversely ; Silurian. 
6. Shell neither spiral nor linear. 
41. GoMPHocBRAS, Sowerby, 1839. = Orthoceras {pars), Sowerby, 1812. = 
Conilites, Pusch, 1837. = Nelimenia, Castelnau, 1843. = Bolboceras, Fischer, 1844. 
= Apioceras, Fischer, 1844. = Poterioceras, M'Coy, 1844. = Lituites {purs) ^ 
Quenstedt, 1846. = Syncoceras [pars), Pictet, 1854. 
Shell straight, pear-shaped ; aperture of exterior chamber contracted, small and 
lobed, the exterior chamber somewhat globular ; position of siphuncle variable ; from 
Silurian into Carboniferous. 
42. Phragmoceras, Broderip, 1839. = Campulites {pars\ Deshayes, 1830. 
= Orthoceratites, Steininger, 1831. 
Shell slightly curved, pear-shaped ; aperture of exterior chamber contracted, small 
and lobed ; siphuncle generally on the internal (concave) side ; from Silurian into 
Devonian. 
43. AscocERAs, Barrande, 1846. = Cryptoceras, Barrande, 1846. 
Shell slightly curved, flask-shaped, lower portion more globular than the upper ; 
partitions of the chambers few and running parallel to the long axis of the shell, leaving 
a space the whole length of the shell for the body of the creature ; aperture of exterior 
chamber not lobed ; Silurian. 
44. Glossoceras, Barrande, 1867. 
Shell same as in Ascoceras, but with the aperture of the exterior chamber lobed ; 
Silurian. 
45. Aphragmites, Barrande, 1867. 
Shell same in general form as Ascoceras, but without several internal partitions ; 
aperture not lobed ; Silurian. 
