182 PALEONTOLOGY OF KENTUCKY. 



Surface, in young specimens, marked by fine elevated striae of growth. The 

 fossils has a diameter of from one to four inches. 



This species occurs usually as internal casts ; in those of older specimens 

 the apex is decollated, and the termination smoothly rounded, as if separated 

 by a septum, no evidence of a continuation above being perceptible. The 

 interior volutions being rounded, the angularity on the upper side is scarcely 

 noticeable before the end of the second volution, and that of the lower side 

 about the same time or a little later. In some of the casts of the interior there 

 is a low, undefined angularity upon the back of the shell. This species ap- 

 pears to be nearly identical with Euomphalus wahlenbergii of Goldfuss (Petre- 

 facta, vol. 3, p. 82, pi. 189, figs. 7, a, &), found in the limestone of the Eifel. 

 That species also presents the same features in the decollation of the earlier 

 volutions, and the rounded apical extremity. That European form is associated 

 with Euomph. planorbis, a species much resembling our Euomph. clymen- 

 ioides, which occurs in the same beds with Euomph. decewi, in western local : - 

 ties. 



Formation and Locality. Found abundantly in the Corniferous limestone in Jefferson county, 

 Ky., and Clark county, Ind. A specimen containing the shell is figured in Geol. Ohio Pal., Vol. 1. 



Euomphalus sampsoni. N. SP. 



Plate XXI., figures 3 and 4. 



Shell discoid, but generally, by apical decollation, receiving the shape of a 

 horn; both sides considerably concave ; the periphery broadly convex. Num- 

 ber of volutions unknown, probably only two. The outer volution rapidly 

 increasing in size; its cross-section near the apex circular, near the aperture 

 oval. The surface is ornamented by from twenty-five to thirty strong, simple 

 plications, each of which extends over the whole length of the outer or last 

 volution, and may probably reach back to the apex. These plications increase 

 in strength from apex to the aperture; their interspaces are also gradually 

 widening in their course towards the front ; they are of unequal width ; some 

 are of four times, and others of double the size of the adjacent ribs. My 

 specimens, being internal casts completely silicified into hornstone, no other 

 surface-markings are retained. 



Form and size of the aperture unknown. This species, with decollated apex, 

 showing only a horn of not quite a whole volution, resembles somewhat Prof. 

 Hall's Nautilus liratus, with which I confounded it, when I found the first 

 specimen, but I soon discovered my mistake. Hall's Nautilus shows plainly 

 the transverse lines of the septae, which do not exist in our shell ; in the latter 

 the curvature is greatly stronger than in the former, and the increase in the 

 size of the outer volution is more gradual in my species than in the Nautilus. 



