162 PALAEONTOLOGY OF KENTUCKY. 



Platyceras compressum. N. SP. 



Plate XXV., figures 8 and 9. 



Shell of medium size or below it ; very compressed in a lateral direction. 

 Apex closely enrolled for one or one and a half volutions, which increase in 

 size very gently ; after this the body-whorl, measuring a little more than a half 

 volution, expands very rapidly in the post anterior direction, while its lateral 

 extension remains almost the same throughout the whole length of the body 

 volution. The right side of the shell is moderately convex in the apical half, 

 but becomes concave in the lower half, the center line of the concavity running 

 at right-angles to the peristome. The left side is throughout concave, but the 

 center line of the concavity is parallel to the peristome, or at least nearly so. 

 The aperture is very elongate and narrow, and expands more or less at the 

 posterior end of its right side. The surface is marked by fine concentric lamel- 

 lose striae, which are closely arranged, especially in the lower half, and by 

 somewhat obscure, shallow, radiating plications, only noticed in the lower 

 part. 



A smaller specimen, of about half the size of the one illustrated, does not 

 show any indications of those plications. The size of the larger specimen is 

 shown in figures 8 and 9, on plate 25. 



Formation and Locality. This beautiful little shell was loaned to me for description and illustra- 

 tion by Major Wm. J. Davis, who found it at the Falls of the Ohio, in the Corniferous limestone, imbedded 

 in the rock, which he removed, without the least injury to the shell, by the use of muriatic acid and para- 

 fine. The smaller specimen he found in the same strata, but already weathered out, in Clark county 

 Indiana. 



Platyceras dumosum. CONRAD. 



Plate XXIII., figures 1 to 6 and 12. 



Platyceras dumosum, Conrad. Third Ann. Kep. of 4th Dist. N. Y. 1840. 

 Platyceras dumosum, Hall. 12th Kegent's Report, p. 19 1859. 

 Platyceras dumosum, Hall. Descript. of New Spec, of Fossils 1861. 

 Platyceras dumosum, Hall. 15th Regent's Report, page 37 1862. 

 Platyceras dumosum, Hall. Illust. of Dev. Foss., pis. 5 and 6 1876. 

 Platyceras dumosum, Hall. Pal. N. Y., Vol. 6, pt. 2, page 141885. 



Shell above medium size ; sub-ovoid ; extremely ventricose in full grown 

 specimens. Its length, from the apex to the anterior margin of the aperture, 

 greater than the height. Apex minute, closely enrolled for a single volution 

 or more, then the body-whorl becomes free and rapidly expanded, spreading 

 more upon the right side, which is sometimes depressed-convex, while the left 

 side is more abruptly rounded. The aperture is sub-rhomboid-ovate, with 

 the peristome making a sinus on the left side, the posterior margin widely 

 separated from the preceding volution. 



