GIRT). THE WEWOKA FORMATION OF OKLAHOMA 151 



When mature, the shell seems to have heen perfectly smooth, without lira? of 

 either sort, except possibly a few revolving ones on the umbilical shoulder. 

 My specimens do not show this sculpture, except here and there, and the fore- 

 going statements are based on scattered observations and not on any one 

 specimen, still less on a series of specimens showing consecutive changes. 



The suture (observed on a shell in an early mature stage) shows a high, 

 narrow ventral saddle, indented on top, and two rounded lateral saddles, the 

 first of which is relatively narrow and symmetrical and the other broad and 

 unsymmetrical. Both are considerably higher than the ventral saddle. The 

 two lobes are tongue-shaped, the inner one being narrow and the outer broad 

 and unsymmetrical. A third, broad, tongue-shaped lobe, smaller than the 

 others, is found on the umbilical zone. 



This species closely resembles Gastriocevas occidentah, the only positive 

 difference of any moment suggested by the description and figures being 

 that the umbilical shoulder of the latter is obscurely crenulated or sub- 

 nodose. As neither the suture nor the sculpture are known, however, 

 adequate grounds for comparison are wanting. 



Horizon and locality : AYewoka formation ; Wewoka quadrangle, Coal- 

 gate quadrangle, Okla. 



Gastrioceras angulatum sp. nov. 



Shell of medium size, subglobose. The largest specimen has a diameter of 

 32 mm. Cross-section trapezoidal, much wider than high. Umbilical shoulders 

 very angular. Umbilicus wide and deep. Ventral surface broadly rounded, 

 more or less parallel to the impressed zone. Constrictions about five to a 

 volution, gently curved across the venter with the convex side forward. A 

 typical specimen has a diameter of 30 mm. with an umbilicus 16 mm. wide. 

 The thickness at the widest part of the final volution is 25 mm. The height of 

 the final volution is 7 mm., the width of the impressed zone 17.5 mm. A 

 small specimen having a diameter of 15 mm. is composed of seven volutions. 



The surface over the venter appears to be smooth when the shell is mature. 

 The region of the umbilical shoulder, however, is marked by moderately coarse, 

 revolving lira?, crossed by about equally coarse transverse lira 3 . This cancel- 

 lated area appears to be narrow and to extend to or just beyond the umbilical 

 shoulder, leaving the umbilical zone smooth. Doubtless in the younger stages, 

 the whole surface was cancellated, though this fact is not shown by my speci- 

 mens. In the later stages also, the transverse cancellating lira? appear to be 

 absent, leaving only a few revolving ones on the umbilical shoulder. 



The suture is not well shown by my specimens. There is a narrow, bifid 

 siphonal saddle with sigmoidal sides. The first lobe is extraordinarily narrow, 

 not so wide as the siphonal saddle and less than half as wide as the second 

 lobe. Both the lobes are tongue shaped. The saddles are rounded, the first a 

 little broader than the second, and they are considerably higher than the 

 siphonal saddle. The umbilical shoulder passes through the outer side of the 

 second saddle and doubtless a third tongue-shaped lobe is situated on the 



