FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 191 



second, and between this and the third, are almost twice as wide as any of the 

 balance. Outside of these mentioned differences there is a complete resem 

 blance between the two specimens. 



Formation and Locality. Found in the cherty layers of the Corniferous limestone, at and around 

 the Falls of the Ohio, in Kentucky and Indiana. This beautiful fossil is exceedingly rare; as far as 1 

 know, Dr. Knapp's and my own specimen are the only representatives of this species. Prof. Hall, who first 

 described and illustrated this species from Dr. Knapp's shell, named it in honor of the late Dr. Lunstbrd 

 Yandell, ST., of Louisville, Ky., who was one of the first collectors of the fossils at and around the Falls of 

 the Ohio. 



Genus Turbo, xiem. 



Turbo, Klein. Tent. Meth. Ostr. 1753. 

 Etymology: turbo, meaning a top. 



Type of this genus is Turbo marmoratus. 



Shells turbinated, solid ; whorls convex, often grooved or tuberculated ; aper- 

 ture large, rounded, slightly produced in front ; operculum shelly and solid, 

 callous outside, and smooth, or variously grooved and mammillated ; internally 

 horny and pauci-spiral. 



This genus extends from the Silurian to the present time. 



Turbo Shlimardi. De VERNEUIL. 



Plate XIX., figures 1 to 4, and Plate XXII., figures 1 and 2. 

 Turbo shuniardi. De Verneuil. Bulletin de la Soc. Geol. de France. 



Shell large, gibbous, sub-globose. Spire moderately elevated ; apex minute 

 volutions about five or six, gradually enlarging in the earlier stages of growth, 

 while the last one increases in size very rapidly, and becomes very ventricose 

 with an expanded aperture. ' The first two or three volutions are smooth and 

 regularly rounded upon the exposed surfaces, gradually becoming nodose and 

 flattened, or somewhat concave, on the upper or front side. The nodes increase 

 in size and strength with the increase of the volutions. Suture close in the 

 earlier volutions and becoming somewhat canaliculate in the later ones. Lower 

 side of the outer volution very convex, even in the umbilical region, and much 

 extended in the direction of the columella. Aperture broadly rounded ; col- 

 umellar lip obtuse, thickened, having a distinct broad opercular groove ; callus 

 covering the umbilicus and spreading outwardly ; external margin of the 

 aperture thin. 



Surface marked by fine, comparatively even striae of growth, which are often 

 crowded into fascicles, and in old shells are somewhat imbricated at irregular 

 intervals. 



The periphery of the outer volution is marked by a strongly elevated, ob- 



