FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 183 



The specimen illustrated on plate 21 is about of average size, and represents 

 the general condition of most of the specimens so far found. 



Formation and Locality. Found in the cherty layers superimposed upon the hydraulic limestone 

 of the Devonian formation, at Watson's Station, in Clark county, Ind., about six miles from the Falls ot 

 the Ohio. This species is named to honor a gentleman who cultivates, not only for himself, different 

 branches of Natural Science, among which most prominently, Geology and Palajontology, but who also 

 endeavors to popularize the same by forming scientific societies in his western home. It is named after the 

 Hon. F. A. Sampson, attorney at law, Sodalia, Missouri 



Genus Platyostoma. conrud. 



Platyostoma, Conrad. Jour. Acad. Nat. Sci. Phil., Vol. 81842. 

 Etymology : platys, broad ; stoma, mouth. 



Mr. Conrad gives the following very meager description of this genus : 

 Shell sub-globose ; spire short ; aperture very large, sub-orbicular, dilated ; 

 labrum joining the body-whorl at right-angles to the axis of shell. The 

 species, Platyostoma niagarensis or P. lineata, may be taken as the type for 

 this genus. The shells of this genus are related to those of Platyceras, with 

 depressed spire, but they differ by the larger number of their volutions and the 

 more gradual increase in the size of the whorls. 



Flatyostoma lineata. CONRAD. 



Plate XXI., figures 7 and 8, and Plato XIX., figures 6, 6, 7 and 8. 

 , Platyostoma lineata, Conrad. Jour. Acad. Nat. Sci. Phil., Vol. 81842. 

 Platyostoma lineata, Hall. Illust. of Devonian Foss., Gast.. pi. 9 1876. 

 Platyostoma lineata, Hall. Pal. N. Y., Vol. 5, part 2, p. 211876. 



Shell above medium size, depressed spiral ; each volution elevated moder- 

 ately above the succeeding one ; number of volutions seldom exceeding four ; 

 apex being usually imperfect. The outer volution large and very ventricose ; 

 it is regularly convex, with the exception of the portion near the suture line, 

 which is generally a little depressed or concave. Aperture sub-rhomboidal, 

 with thin outer lip and a sharp entire margin ; columellar lip thickened, folded 

 and renexed over the umbilicus, which is entirely closed in adult speci- 

 mens. 



Surface marked by fine, nearly equidistant, thread-like revolving striae, as 

 seen in figures 5 to 8, plate 19. which are cancellated by fine concentric striae 

 of about the same strength, but of unequal distance ; the latter sometimes 

 bend abruptly backward upon the back of the shell, indicating a sinus in the 

 lip at some period of growth, and are frequently crowded in fascicles, giving 

 a rugose appearance to the surface of the shell. In well preserved specimens 

 the surface is beautifully cancellated; and in worn and partially exfoliated 



