94 NEW SILJJRIC GASTROPODS 



Barrande's work in Bohemia and has decribed the specimens 

 subsequently found, accepts the new name proposed by Kayser, 

 not, however, for any of the reasons given by the latter author, 

 but on philological grounds, for if the name Pilidion were 

 latinized it would become the homonym of Pilidium Forbes. 

 For this reason only does Perner replace Pilidion Barrande by 

 Hercynella Kayser. Since the species bohemica was the type for 

 Barrande's genus, it remains the type of Hercynella. 



So far as known, the geologic range of Hercynella is small. 

 Furthermore, it has been recorded from only three localities ; 

 the first is Bohemia, from which fifteen species have been 

 described, some by Barrande, the rest by Perner; the second is 

 Harz mountains, where Kayser found two species ; and the third 

 is in America in the Monroe formation of Michigan from which 

 Grabau described one species. Hercynella canadensis Grabau is 

 represented by a single incomplete specimen, but much interest 

 attaches to it, since it is the only member of the genus which 

 has heretofore been described from this country, and the very 

 fact of its occurrence has probably been noted by few. It is, 

 then, of considerable interest to find in a still earlier horizon in 

 this country several specimens of this rare genus Hercynella, 

 making a new locality and horizon in America and the fourth 

 locality in the world. 



The typical Hercynella is a patelliform, non-spiral gastropod, 

 having the apex of the shell asymmetrically situated, and varying 

 in form from a low cone to a flat inverted basin with very gently 

 sloping sides. The characteristic of especial importance is a 

 radial depression passing from the sub-central apex to the border, 

 and bounded upon one side by a pronounced angulation in some 

 cases, but in others merging imperceptibly into the general 

 curvature of the shell. In most descriptions the angulation is 

 the feature which is emphasized, whereas in reality it is the 

 depression or sinus which is marked, since the shell growth in 

 the majority of cases follows a definite curvature and then makes 

 a sudden drop, forming the sinus, beyond which the shell 

 continues at a lower curvature. For this reason it seems 

 advisable to lay stress upon the sinus, not the ridge, since the 

 latter is related to a true fold or ridge in the same way that a 

 monoclinal flexure is related to an anticline. It would be only 

 in the case of a ridge rising above the general curvature of the 



