GIRTY, THE WEWOKA FORMATION OF OKLAHOMA 149 



ficial deposit, whether intrinsic or extrinsic I am unable to determine. This 

 makes the surface look either smooth or, as the sculpture shows through, 

 marked by obscure lines of increase. The lirse, which seem to strengthen and 

 coarsen as they cross the ventrolateral shoulders, form a deep sinus on the 

 venter. On the sides the direction is sigmoidal, convex above and concave 

 below ; similarly on the umbilical zone, save that the concave portion, which is 

 below, is very slightly developed. When mature, the ventrolateral shoulders 

 are marked by small, rather indistinct nodes. 

 Suture not known. 



This species is of the type of M. ivalcotti and M. liayi. From both spe- 

 cies it seems to differ in having the height proportionately less in com- 

 parison with the width ; in having the sides contract toward the venter ; 

 in having the umbilical zones more nearly horizontal and the umbilical 

 shoulders perhaps a little more angular. The nodes along the ventro- 

 lateral angles appear to be smaller and less distinct than in M. hayi, 

 while the sculptured surface of M. sculptile is not recorded for either 

 species. 



Horizon and locality: Wewoka formation; Wewoka quadrangle, Okla. 



Cyrtoceras peculiare sp. nov. 



Shell rather small, expanding with extreme rapidity. Apical angle about 

 60°. Axis nearly, if not quite, straight. The rate of expansion is so great 

 that unless the shell grew to a very large size, the curvature of the axis would 

 hardly be preceptible. The sides, therefore, appear to be nearly straight, but 

 that on which the expansion is least rapid may probably be regarded as the 

 dorsal and the other as the ventral side. The siphuncle then is strongly dorsad. 

 The cross-section would be broadly oval, contracting toward the dorsal side, 

 which is somewhat flattened. Only five chambers are preserved, the oldest 

 being about three times as high as the others. The prolongation of the cham- 

 bers is so rapid on the ventral side that in the internal mold they make step- 

 like projections. The sutures are nearly direct, but are more or less distinctly 

 sinuated, with gentle lobes on the dorsal, ventral and lateral surfaces, and 

 equally faint saddles between. 



The extremely rapid expansion of this species distinguishes it from the 

 few Carboniferous representatives of the genus known in North America. 

 It is, however, very doubtful whether this is a true representative of 

 Cyrtoceras, a question which can be raised with equal propriety regarding 

 the other American Carboniferous species referred to the genus. 



Horizon and locality : Wewoka formation ; Wewoka quadrangle, Okla. 



Gastrioceras venatum sp. nov. 



Shell small, attaining a diameter of IS mm., compressed globose. Umbilici 

 rather large and open. Whorl section lunate, somewhat tumid at the sides 

 with an ill-defined \unbilicnl shoulder. 



