Newell. 1 478 [Jan. 18, 



partly broken. The portion of the shell enclosing the dorsal open- 

 ing extends upward so that the aperture faces toward the rear, and 

 is surrounded by a flaring collar. On one side of the lower edge 

 of this, there is a slight indentation indicating that this aperture 

 may have been lobed. • 



The air chambers are unknown. The sutures, as shown by the 

 base of the living chamber, have sharp, ventral saddles, broad, 

 low, dorsal saddles and wide lateral lobes. 



The siphon, test, and surface markings are not preserved. 



The type specimen above figured is undoubtedly peculiar in the 

 unsymmetrical form of the aperture. The long narrow slit, instead 

 of being median, has a decided curve to one side of the centre, 

 which, evidently from the symmetry of the rest of the figure, can- 

 not be due to compression. 



Fine striations can be seen on portions of the cast. The course 

 of these striations is indicated in a general way by the oblique 

 lines on the figures. 



The dimensions are as follows : dorsi-ventral diameter of the 

 last septum, that forming base of the living chamber, is 30 mm. ; 

 diameter just below the apertures 40 mm. ; lateral diameter on this 

 section 23 mm. ; height along the vertical central axis 37 mm. 



G. parvum H. & W. is smaller, and possibly may be the young 

 of the same species. The region in front of the dorsal opening 

 apparently does not rise as in G. projectum making the top of the 

 latter somewhat concave in lateral view. Also the curve of the 

 shell under the ventral tube in G. projectum is more gentle than 

 in G. parvum. G. nestor Hall differs in the dorsal opening facing 

 upward and not to the rear. 



G. labiosum Ban*, has a smaller ventral opening, and greater lat- 

 eral diameter of the living chamber, also the distance from the 

 ventral opening to the last septum is proportionally greater. 



Locality. — Delphi, Indiana. 



Genus HEXAMEROCERAS Hyatt. 



This genus includes Silurian species of Gomphoceratidse which 

 have the dorsal aperture constricted in such a manner as to leave 

 six lateral sinuses, arranged in three pairs symmetrically as to 

 dorsi-ventral plane of the animal. 



