BUFFALO SOCIETY OF NATURAE SCIENCES 



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shell and not bounded on either side by a sinus, as in H. 

 rigescens from the middle Devonic G, of Bohemia or in the case 

 of two radial depressions with fold between, of which however, 

 there is no known instance, that we could truly speak of a radial 

 fold or crest. In none of the material from Bohemia which I 

 have examined, and in only a few of the illustrations of Hercynella 

 have I seen a true ridge, but in most cases there was only a 

 monoclinal flexure, such as is well illustrated in H. radians Barr. 

 sp. from F, of Bohemia (fig. 2). In the most high coned forms 

 the sinus is, as a rule the deepest, while in those which have a 

 lower cone, approaching a very flat patelloid condition, the 



Fig. 1. Outline of Hercynella regescens Barr. sp. from G, of Bohemia, 

 x4/o. 



Fig. 2. Outline of Hercynella radians Barr. sp. from F, of Bohemia, 

 showing the young stages as indicated by the growth lines, x 4/5. 



sinus is shallower and may, indeed, be hardly noticeable. 

 With the variation in depth of the sinus there is an accompany- 

 ing variation in the marginal outline of the shell, forms with a 

 pronounced sinus having a sharp re-entrant, while flatter ones 

 show a shallow re-entrant approaching an entirely convex 

 curvature for the whole periphery. The surface of the shell 

 bears concentric lines of growth and frequently ribs, which in 

 some cases are quite pronounced. Some species also show radial 

 striae. 



