150 GASTEROPODS. 



Shell of medium size, globose, dorsum broadly rounded ; 

 umbilici closed ; aperture transversely semilunate, but not ex- 

 panding much more rapidly than the uniform enlargement of 

 the volutions ; inner lip but slightly developed; outer lip thick- 

 ened and rounded toward the umbilici, but becoming very at- 

 tenuated medially ; its central sinus rather broad, rounded and 

 not very deep. Medial band obscure on the costate portion of 

 the shell, but on the terminal half of the body whorl more or 

 less distinct, and in some specimens bordered on each side by a 

 low, narrow, yet well-defined ridge. Surface, except the last 

 half of the outer whorl, ornamented with from 16 to 30 or more 

 sharp, simple, nearly parallel eostse; terminal half of the body 

 whorl generally glabrate, except along the medial portion, which 

 is often marked by lines of growth, and sometimes by two lon- 

 gitudinal angularities. Often the greater part of the smooth 

 area is covered with small but well-defined tubercles. 



Horizon and localities. Upper Carboniferous, Upper Coal 

 Measures : Kansas City. 



The form considered here under the name of ftellerophon 

 urii is the one usually designated by American palaeonto- 

 logists as B. carbonarius. A. careful comparison of the de- 

 scriptions and figures of the various writers on this group of 

 Gasteropods, and of a large series of specimens fails to furnish 

 any valid reasons for separating specifically the American form 

 from the European shell described by Fleming in 1828 as Belle- 

 rophon urii. Norwood and Pratten correctly referred the 

 specimens collected by Cox in Kentucky to B. urii; but Cox 

 in 1857 made them the types of a species which he called B* 

 carbonarius^ distinguishing it from the European form by the 

 slight lateral expansion of the mouth, and particularly by the 

 less number of revolving costae, which in B. carbonarius were 

 said to vary from nineteen to twenty-five, while, according to 

 de Koninck, B. wmhad from thirty-six to thirty-eight. Though 

 de Koninck does make this latter statement in his earlier work, 

 his later Eecherches state that the number varies from twenty- 

 two to thirty. McChesney,in the description of his B. Uaney- 

 anus, seems also to have made the chief distinctive character 



