568 PALEONTOLOGICAL REPORT OF GEOLOGICAL SURVEY. 



lique mesial sinus extends to the base, where it becomes profound; base 

 emarginated; hinge area straight, almost forming a right angle with 

 the posterior margin which is nearly straight; slightly sinuate above; 

 obtusely rounded below; upper posterior part obliquely truncated; 

 surface covered with concentric lines marking stages of growth, and 

 fine radiating ribs, numbering on the disk about seven in one and a 

 half lines; width l. T Vo inches, height . T 6 T 9 ,- inch. 



Position and locality. Rather abundant in the limestone over the 

 main coal No. 11, at Providence, Hopkins county; also in a limestone 

 over an equivalent coal on the property of Edward and William Hawes, 

 near Hawesville, Hancock county, Kentucky. 



GERVILLIA LONGISPINA. Cox. 

 (PI. VIII, fig. 6, left valve natural size.) 



Lunate; hinge area straight; posterior ear defined by a deep sinus; 

 hollowed out on its lateral margin, and terminated by a long spine; 

 beak depressed, pointed; anterior margin and base together form a 

 semicircle; eliptically pointed at the posterior extremity; posterior 

 border slightly concave, from which rises an abrupt ridge, gradually 

 declining to the base and anterior border; anterior ear wanting; sur- 

 face covered with fine strise and strong marks of growth; length from 

 beak to posterior extremity l. T W inches, height .— 3 7 inch. This re- 

 markable species has no analogy with any other with which we are 

 acquainted. A portion of the spine has been restored from fragments 

 found in the rock. 



Position and locality. Not uncommon in the limestone which over- 

 lays the main coal No. 11, at Providence, Hopkins county, Kentucky. 



PLICATULA STRIATO-COSTATA. Cox. 



(PI. VIII, fig. 7; right valve natural size.) 



Triagonal; inequilateral; right valve moderately convex; from nine 

 to ten large elevated ribs arise irregularly below the beak, increasing in 

 size to the circumferance, separated from one another by deep furrows, 

 crossed about one-third the length above the base by an irregular con- 

 centric groove, below which, on the anterior side, the ribs are slightly 

 bent forward, giving the appearance of having been broken ; above this 

 are two other rather indistinct bands; surface and ribs covered with 

 fine irregular thread-like strise, increasing by intercalation, rising from 



