Ciiiciiuiafiaii and Lexington Fossils 55 



the types, since the latter are labelled as coming- from Cincinnati 

 Ohio. 



HchcrtcUa subjngata, in the Eden, appears to be a direct 

 descendant of Hcbcrtdla parkscnsis, from the Greendale division 

 of the Cynthiana formation. Hcbcrtella occidcntalis is regarded as 

 a descendant of Hcbcrtella subjngata, with Hcbcrtella sinuata as 

 another derivative. 



Hebertella alveata — richmondensis. 



(Plate V, fig. lo.) 



In typical Hcbcrtella alveata (this Bulletin, vol. XIV. plate 

 IV, fig. 8A), the shell is considerably wider along the hinge-line 

 than anteriorly, the postero-lateral angles being acute. In the A-ariety 

 richniondensis\ plate V, fig. 10, the hinge-line is considerably 

 shorter than the width of the shell across the middle, the postero- 

 lateral angles are rounded, and the brachial valve is strongly con- 

 vex, especially in the umbonal region. Both forms occur in the 

 upper part of the Whitewater bed, at Richmond, Indiana, accom- 

 panied by intermediate forms (plate V, fig. 17). It is very doubt- 

 ful whether the forms with a very short hinge-line shoulcl be dis- 

 tinguished even as a varieiiy. Hcbcrtella ahwita makes its appear- 

 ance already in the Liberty bed, although Hcbcrtella occidcntalis, 

 characterized by the slight median depression at the beak of the 

 brachial \ahe, disappearing anteriorly, is far more common there. 



Platystrophia colbiensis, sp. nov. 



(Plate IV, figs. 2 A, B.) 



In the Cynthiana formation, between Colby and Winchester, 

 in Kentucky, a small form of Platystropliia occurs in which the 

 median fold is only mo;lerately elevated, and not strongly com- 

 pressed laterally, while the sinus is iM'oad and shallow. Four plica- 

 tions occupy the fold, and three occur in the sinus. The number 

 of lateral plications on each side of the fold varies usually from 8 

 to 9. The hinge-line may ecpial the width of the shell across the 

 middle, but usually is a little shorter. The convexity of the shell 

 is considerable, but rarely enough to be called gibbous. Owing to 

 the small elevation of the fold, the brachial \'al\-e has a more 

 evenlv convex appearance than the small forms of Platystrophia 

 occurring in the Mount Hope bed, and described by Meek under 



