CEPHALOPODA. 
4 49 
to be simple inflexion over the sides of the volution, without indicating any 
deviation from the ordinary nautiloid curve, and except for the narrow 
ventral lobe, the generic character would not be recognized. The siphuncle 
is small, situated just beneath the ventral surface, its walls coincident with 
the narrow lobe penetrating the preceding volution, and having a diameter 
of a little more than one mm. 
Test thin, having a thickness not exceeding .5 mm.; usually obliterated 
in the specimens. Surface marked by sharp, transverse striae, of which there 
are about seven in the space of three mm., with flat interspaces which are 
marked by extremely fine strim. The striae curve gently backward over the 
' sides of the periphery; but the sinus in strire or aperture has not been 
observed. A single, partial cast, preserving a little of the inner layer of the 
shell, shows fine, longitudinal striae, which are apparently a part of the shell- 
structure. The internal cast is smooth, showing strongly impressed suture 
lines. The moulds of the exterior have shown the lateral subangular margin 
to be ornamented by a series of nodes, which, also, are sometimes preserved 
in the casts of the interior. The specimens present a gradation in size from 
those having a diameter of forty-five or fifty mm. to others measuring nearly 
100 mm. in their greatest extent. 
This species bears little resemblance to any forms known in the rocks of 
New York ; but is closely related to G. plebeius , Barrande (ut cit.), and assumes 
the great variety of form and expression which are so fully illustrated in the 
figures cited. The volutions in the Bohemian species are more numerous than 
in ours, and increase in size more gradually, while the septa are comparatively 
more distant. 
In the New York specimens it has thus far proved impossible to obtain any 
satisfactory knowledge of the inner volutions, all the specimens which have 
been cut for this purpose showing scarcely anything more than is illustrated in 
figures 7 and 8 on plate 110. The inner volutions have usually been entirely 
dissolved by the action of iron pyrites, or have been broken up and irregularly 
disposed in the cavity, as shown in figure 9. Figure 4 of the same plate is 
from a gutta-percha impression in the cavity left by the partial solution and 
57 
