218 PALAEONTOLOGY OF KENTUCKY. 



Modiomorpha charlestowuensis. v M-. 



Plato V., figures 7, 8 and 9. 



The shell illustrated on plate 5, figures 7, 8 and 9, has evidently its valves 

 dislocated. The right valve is more than one-eighth of an inch removed back- 

 ward. 



Shell of about medium size, elongate, sub-elliptical, very ventricose or gib- 

 bous; greatest height at about one- third of length from the anterior extremity ; 

 valves strongly convex, the greatest convexity being a little anterior to the 

 middle of shell. Hinge-line oblique, almost straight, and of about one-half 

 the length of shell. Beaks anterior or sub-anterior, acute and closely ap- 

 pressed. Umbonal region strongly convex, angular, and inflected on its dorsal 

 slope near the beaks, regularly curved on its ventral and posterior slopes, and 

 also in the posterior half of its dorsal slope ; prominently ridged. The course 

 of the umbonla ridge forms an acute angle with the cardinal line, and runs 

 somewhat diagonally to the posterior extremity, where the post-ventral and 

 post-dorsal margins meet in a very abrupt curve. 



Ventral or basal line almost straight, only slightly incurved in its central 

 portion ; at its posterior end it curves regularly and gently upwards into the 

 abrupt curve at the posterior extremity. The posterior part of the dorsal line 

 forms a gentle regular curve from posterior end to hinge-line 



Anterior end short, its margin straight and sloping almost rectangular with 

 the cardinal line down to the basal margin, which it meets in a short curve. 



Surface covered by fine concentric lines of growth, which, at irregular inter- 

 vals, have been raised into imbricating lamellae, leaving strong varices on the 

 cast. 



A portion of the shell remaining shows the concentric lines as closely set as 

 on Mod. concentrica, and if the form of my shell did not differ so greatly from 

 that of Mod. concentrica, I would have placed it with that species. Its elon- 

 gate form, its great gibbosity, its linguiform posterior end, and the marked 

 concentric zones on its surface, distinguish it from its other congener, with 

 which it is associated in our rocks. 



Formation and Locality. The chert beds over the hydraulic limestone of the Devonian formation 

 in. Jefferson county, Ky., and in Clark county, Ind. 



