GIRTY, THE WEWOKA FORMATION OF OKLAHOMA 139 



Our well-known Pennsylvaniau species B. crassus and also the Upper Missis- 

 sippian B. sublcevis are therefore typical Bellerophons. 



We have in onr Pennsylvaniau faunas a species, or perhaps a series of 

 mutations, which presents well-marked differences from the characters pos- 

 sessed by typical Bellerophon, so that a subgeneric separation is justified, if 

 aot demanded. The dorsum is elevated into a prominent nodose carina on 

 which traces of a slit band seldom remain. Many specimens therefore appear 

 to lack such a structure altogether and to be related to the Indian Warthia 

 and Mogulia. Some specimens retain unmistakable traces of a band, how- 

 ever, and there can be little doubt that this structure is a normal feature of 

 this type. That it is obliterated so often is probably due to its prominent 

 position and also perhaps to the tumid condition of the median line of the 

 dorsum. 



From Bellerophon this type also differs in the development of coarse, heavy, 

 angular, transverse plications, quite distinct from the growth lines, which are 

 not conspicuous, these plications being also in some cases strengthened at two 

 series of points, one on each of the sides, so as to form more or less promi- 

 nent nodes (connected in some cases by revolving ridges). The linear arrange- 

 ment of these nodes produces two carina? additional to the median one which 

 is the locus of the slit band. 



Type species. Bellerophon percarinatus. 



Meekospira peracuta var. choctawensis var. nov. 



This fossil is very abundant in the Wewoka formation and shows certain 

 variations, some of which are probably adventitious. It has an acutely conical 

 form with a very elongate spire and a narrow spiral angle. The sides are 

 usually flat with the suture only slightly depressed, but not infrequently the 

 sides of the spire are more undulating and the suture deeper. This is per- 

 haps due to variation in curve of the outer surface of the whorl. In the one 

 case the convexity is more regular ; in the other, the upper surface of the 

 volution is flattened and the greatest convexity well below the middle, where 

 it is overlain by the succeeding whorl. The rate of increase seems to be 

 accelerated somewhat toward maturity, so that the sides of the spire are 

 slightly concave. As a result, when the apex of specimens is broken away, 

 which very often happens, the frustum remaining appears to have a wider 

 spiral angle than was really the case. In comparing these with more perfect 

 specimens, one is somewhat surprised to find that they may belong to the 

 typical variety, as well as to find what a large number of volutions is present 

 when the apex is complete, the number being proportionately much greater 

 toward the top. On the side of a specimen 14 mm. long, parts of nine volutions 

 appear and as the apex is broken, there must have been one or two more. A 

 full-sized specimen about 30 mm. long shows parts of ten volutions with an 

 apical break which may possibly account for two more. The number of com- 

 plete volutions in a mature specimen is probably eleven and possibly twelve. 



The callus is a very distinct character in well-preserved specimens, extend- 

 ing half way or a little less than half way up the inner lip. It is formed by 

 a slight backward flexure on itself of the outer lip as it passes up the axis 

 and is there gradually lost in the aperture. 



