38 Trans. Acad. Sci. of St. Louis. 



up to the anterior end of the hinge-line; posterior margin 

 more narrowly rounded at its most posterior extension and 

 nearly straight above, where it slopes up to the hinge-line. 

 Hinge-line slightly arcuate, more than one-half the total length 

 of the shell. Valves regularly convex, the greatest depth 

 beinof about one-fourth of the height. Beaks rather small 

 and incurved, situated at about the anterior fourth of the 

 total length of the shell. Surface marked by more or less 

 inconspicuous concentric striae. 



Remarks. This shell may be easily distinguished from the 

 last by its smaller size, by its more pointed posterior extremity, 

 and generally by its smoother surface. 



GASTEROPODA. 

 Bellerophontidae . 



No less than sixteen species of this family have been de- 

 scribed from Iowa, Ohio, Michigan, etc., from strata of about 

 the age of the Vermicular Sandstone, but of these only six 

 have been illustrated, and in most cases even these have not 

 been illustrated from typical specimens. Under these circum- 

 stances it is exceedingly difficult to identify with any certainty 

 the species of the genera included in this family. American 

 writers have almost universally included all the Bellerophon- 

 tidae in the single genus Bellerophon^ but several very dis- 

 tinct groups of shells have obviously been included in this 

 genus. In his monograph of the Carboniferous fossils of 

 Belgium, De Koninck* has recognized seven genera among the 

 carboniferous Bellerophontidae of Belgium, and his generic 

 divisions will be used in this paper. 



Among the Northview fossils, at least four species, belong- 

 ing to as many genera, of BelleropJiontidae have been collected. 

 All the specimens are imperfect to a greater or less degree so 

 that certain identification would be difficult even were the 

 known species well illustrated, but under the circumstances 

 it is impossible to be sure whether some of the Northview 

 specimens belong to already described species or whether 



♦ Faun, du Calc. Carb. de la Belg. pt. 4. Gasteropods. 



