7 4 NAuiriLOIDEA. 
Genus HERCOCErA^S, Barrande ^ (restricted. 
{GyroeeraSj Barrande, 1854 Nautilus, Barrande, 1856; 
Nautilus, BBake, 1883 
Oen. Char. Shell discoid, whorls very slightly emhracag, 
quadrate in section ; umbilicus wi de, rather shallow, exj)sing all 
the volutions. Body- chamber eqtialling about half theiength of 
Fig. 
sub- 
Hercoceras mirum, after Barrande, — a, laterii.1 view, showing tbe stumps of the 
spines and a few septa ; h, front view, elbowing the pecular position and 
contracted form of the aperture. Somt^ of the test is seen at the lower 
part of the figure. Copied from pi. cccc Ixxvii. case 2, 'of the Syst. Sil. de 
la Boheme, voL ii. Suppl. et Serie tardive,!* 1877. The figures are reduced 
from figs. 3, 4, pi. xlii. (vol. ii.) of the samse work. 
the last whorl. Aperture much contrac 'ted by the inflexion of its 
margin, occupying the upper | of the '.xtremity of the whorl, and 
extending obliquely backwards so as to c ut off a considerable portion 
of the convex border. This peculiar posution of the aperture is due 
to the existence of a diaphragm, perp'endicular to the axis and 
closing the extremity of the whorl tra nsversely. Septa simple, 
moderately concave. Siphuncle cylindrica’ 1, situated very near the 
peripheral margin. Surface of the test oflnamented. with a row of 
strong, hollow spines along the lateral angf.e of the whorls ; trans- 
verse lamellose striae are also present, and f brm a conspicuous sinus 
upon the periphery. ; 
(r 
^ Defenses des Colonies, 1865, iii. p. 31 ; Sys 4. Sil. d( ) la Boheme, vol. ii. 
1867, p. 152. 
^ Leonhard and Bronn’s Jahrbuch, Heft i. p. 7, "pi. i. 
^ Bull. Soc. Geol. de Trance, vol. xiii. p. 383. |i i* 
^ British Foss. Ceph. pt. i. p. 62. ji 
I i 
