‘ 
54 NAUTILID. 
Shell straight, conical; a small sutural lobe corresponds to 
the marginal siphon. 
Prioceras, Salter, 1859. 
EHtym.—Pilos, a cap, and ceras, a horn. 
Distr.—Fossil, 3 species. L. Silurian; Canada, Scotland 
(Ideal section, xxx, 97). 
Shell broad, conical, subeylindrical or compressed, slightly 
curved. The siphuncle and septa represented by a series of 
conical septa, concave to a central point. Closely related to 
Cyrtoceras. 
Cyrroceras, Goldfuss, 1832. 
Etym.— Curtos, curved, ceras, a horn. 
Syn.—Aploceras, d’Orb., 1850. Campulites, Desh. (part), 1832. 
Campyloceras and Trigonoceras, M’Coy, 1844. 
Distr.—Fossil, 350 species. lL. Silurian to Carb.; N. and S. 
America, Europe. C. acuticostatum, Sandb. (xxx, 98). 
Shell curved ; siphuncle small, subcentral. 
Seems to differ but little from Orthoceras. 
ONCOCERAS, Hall, 1847. (Oncos,a protuberance, ceras,a horn.) 
Anterior half of the shell inflated, aperture more or less stran- 
gulated. This may possibly = Phragmoceras, Brod. Distr.— 
3 sp. Silurian; New York. O. constrictum, Hall (xxx, 997). 
CYRTOCERINA, Billings, 1865. Shell short and thick, with a 
large siphuncle, placed externally. Distr.—2 species. Silurian ; 
Canada. 
STREPTOCERAS, Billings, 1865. Shell like Oncoceras, but the 
aperture trilobed. 2 species. Middle Silurian; Canada. 

GompHoceras, J. Sowb., 1839. 
Etym.—Gomphos, a club, and ceras, a horn. 
Syn.—Apioceras, Fischer, 1844. Poterioceras, M’Coy, 1844. 
Mesoceras, Barrande, 1877. Bolboceras, Fischer, 1844. Neli- 
menia, Casteln., 1843. 
Distr.—100 sp. L. Silurian to Carb.; Europe, N. America. 
G. pyriforme, Murchison (xxx, 100). Silurian; England. G. 
Bohemicum, Barr. (xxx,1). Aperture. 
Shell fusiform or bottle-shaped, straight, swollen nueeconle ; 
aperture contracted in the middle ; siphuncle subcentral; septa 
simple, concave. 
SycoceRas, Pictet, 1854. 
Distr.—Silurian, Devonian. S. orthogaster, Sandb. (xxx, 21). 
Shell oval or bottle-shaped, straight; septa simple; siphuncle 
marginal. 
The position of the siphon varies so much in this group, that 
it is an insuflicient character to distinguish the genus from 
Gomphoceras. 
