CEPHALOPODA. 449 



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 stria), of which there 

 are about seven in the space of three mm., with flat interspaces which are 

 marked by extremely fine striae. The striae curve gently backward over the 

 sides of the periphery ; but the sinus in striae 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. pkbeius, Barrande (ut tit.), 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 



