52 NAUTILID&. 
into its shell, as in the Nautilus. That the shell was external is 
indicated by the colored bands preserved on O. anguliferus. 
These shells sometimes grew to a great size; a specimen in the 
collection of Mr. Tate of Alnwick, England, must have been six 
feet long when perfect. Newberry, in the Paleontology of Ohio, 
estimates another species, O. Zitan, to have weighed ‘some 
tons.” The aperture is sometimes so contracted that species 
two feet in length have a diameter of only one inch at the mouth. 
CAMEROCERAS, Conrad, 1842. (Melia, Fischer; Sannionites, 
Fischer.) Siphuncle lateral, sometimes very large (simple?). 
Casts of the large siphuncles were called Hyolites by Eichwald. 
Distr.—27 sp. lL. Silurian to Triassic (?); N. America, Europe. 
ACTINOCERAS (Brown), Stokes. Siphuncle very large, inflated 
between the chambers and connected with a slender central tube 
by radiating plates. 6sp. L. Silur. to Carb.; N. America, Europe. 
O. Richardsoni, Stokes (xxix, 78). 
ORMOCERAS, Stokes, 1838. Siphuncular beads constricted in 
the middle, so that the septa appear as if united to the centre of 
each. Probably identical with Actinoceras. Distr.—3 sp. lL. 
Silurian to Devonian; N. America. O. Bayfieldi, Stokes (xxix, 
84). 
HURONIA, Stokes, 1823. (Discosurus, Hall, 1852.) Shell ex- 
tremely thin, membranous or horny (?). Siphuncle very large, 
central, upper portion of each joint inflated, connected with a 
small central tube of radiating plates. Usually the siphuncle 
only is preserved. Dr. Bigsby observed specimens six feet in 
length. Doubtfully distinct from Actinoceras. Distr.—3 sp. 
L. Silurian; Drummond Isl., Lake Huron. H. vertebralis, Stokes 
(GexIx, 85): 
AULACOCERAS, Hauer. Shell much thickened, longitudinally 
furrowed, with two deep lateral sulecations ; siphon very small, 
marginal. Distr.—4 sp. Upper Triassic; Austria. 
BATHMOCERAS, Barrande, 1865. Part of the body-chamber 
occupied by imbricating plates, decreasing in horizontal exten- 
sion from below upwards; siphuncle a series of superimposed 
funnel-shaped tubes. Distr.—4sp. Silurian; Bohemia, Sweden, 
Lake Huron. 
ENDOCERAS, Hall, 1847. (Conotubularia, Troost; Diploceras, - 
Conr.) Shell extremely elongated, cylindrical. Siphuncle very 
large, cylindrical, lateral; thickened internally by repeated 
layers of shell, or partitioned off by funnel-shaped diaphragms. 
Distr.—12 sp. L. Silurian; New York, Europe. 
TRETOCERAS, Salter, 1858. (Diploceras, Salter, not Conrad, 1856; 
Nothoceras, Hichw., 1859.) Founded on O. bistphonatum, Sowb. 
(xxx, 93), from the Caradoc sandstone (Silurian), Brit.,in which 
the septa are apparently perforated by two siphuncles; one of 
which is a deep lateral cavity continuous with the terminal 
