246 
NATJTILOIDEA. 
Genus SEPTAMEROCERAS, Hyatt ^ 
Gen. Char. Shell with seven lobes in the larger orifice of the 
aperture. 
Type, Gomphoceras injlatum, Billings, sp. ^ 
Family ASCOCERATID^ ^ 
Genus ASCOCERAS, Barrande ^ 
{Cr^ptoceras, Barrande, 1846^, ?ion d’Orbigny.) 
Gen. Char. The shell is of a sac-Uke form, essentially straight, . 
but always more convex on the ventral than on the dorsal side. 
The apex is unknown, the shell being always truncated. The 
transverse section may be elliptical or circular. The body-chamber 
occupies nearly the whole length of the shell on the ventral side, 
and contracts into a neck-like prolongation towards the aperture, 
which is simple. The last few septa are abnormal ; they have the 
usual shape and position on the ventral side of the shell, but on the 
dorsal side they coalesce, and sweeping upwards in a sigmoid curve 
(as seen in section, fig. 41, a) form a series of vaulted chambers 
convex towards the aperture, and encroaching considerably upon the 
body-chamber. This extraordinary conformation of the septa on the 
dorsal side was doubtless caused by the shrinking of the animal in 
its shell on that side, whereby a cavity was created between the 
shell-wall and the mollusk, and then partioned in the manner above 
described. The short siphuncle is submarginal and near the ventral 
or concave border of the shell ; it diminishes rapidly in size towards 
the body-chamber. The test is relatively thick considering the size 
^ Proc. Boston Soc. Nat. Hist. vol. xsii. 1883, p. 278. 
^ I have failed to find any species described by Billings under this name. It 
is not in S. A. Miller’s Cat. of Amer. Pal. Foss. I have therefore figured 
Se^tameroceras septoHs, Hall, sp. (fig. 40, c). 8. septoris is described and 
figured in the 18th Eegent’s Hep. on the New York State Cabinet of Nat. Hist. 
1864, p. 350. 
^ Comprising the genera Ascoceras, Glossoceras, Billingsites (?). 
^ Oesterr. Blatt. fiir Litt. u. Kunst, 1847, and Haidinger’s Berichte fiber d. 
Mittheil. v. Freund, d. Naturwiss. in Wien, 1847, p. 268, also Bull, de la Soc. 
Geol. de France, 1856, ser. 2, vol. xii. p. 157. 
® Notice prelim, sur le Syst. Sil. et les Trilobites de Bohdme, 1846, p. 43. 
