120 PALEONTOLOGY OF KENTUCKY. 



gibbosity of the shell gives an apparent variation in the height of the area ; 

 the beaks of the two valves sometimes approach very close to each other. 

 (Hall.) 



Formation and Locality. This species is found abundantly in the Corniferous limestone at and 

 around the Palls of the Ohio in Kentucky and Indiana. It appears here silicified, in well preserved 

 specimens of the whole shell, as well as of the separated single valves. Specimens still inclosed in the 

 limestone are of the same material. From observations made by me at the Falls of the Ohio, and which, 

 undoubtedly, were also made by other geologists, who visited and examined that world-renowned store- 

 house of Devonian fossils, but of which I never found any notice in print, I am forced to the conclusion 

 that the silicification of the shells and corals is produced by their exposure to water and weather, and that 

 this process requires only a comparatively short time. Whenever, at low stages of the water, the bed of 

 the falls becomes dry, we find it entirely covered by fossil shells and corals, partly exposed above the solid 

 rock and partly inclosed in the same. All the exposed fot>sils which have been acted upon by water and 

 weather for some length of time are silicified, as far as they are above the matrix, while the inclosed 

 parts are still limestone, or, if a change in their material has already commenced, the silicification has 

 not sufficiently advanced to resist the dissolving power of muriatic acid, which has not the least influ- 

 ence upon the exposed parts. In the same condition are the fossils found in the fields near the falls 

 in Kentucky and Indiana. Those which are entirely weathered out, and the parts of others freed from 

 the matrix, are silicious, while the inclosed parts have retained their original material. 



Spirifera grieri. HALL. 



Plate IX., figures 8 to 14. 



Spirifer grieri, Hall. Tenth Rep. on State Cab., p. 127 1857. 

 Spirifer grieri, Hall. Pal. N. Y., Vol. 4, p. 194, plates 27 and 23. 



Shell gibbous, transversely oval or sub- quadrilateral, sometimes longitudi- 

 nally ovate, the proportion of length and breadth being very variable ; hinge- 

 line considerably shorter than the greatest width of the shell ; cardinal 

 extremities rounded. Valves sub-equally convex. 



Ventral valve gibbous or ventricose ; most convex above the middle, and 

 nearly opposite the center of the hinge-line, and sloping somewhat abruptly 

 to the lateral margins, but more gently to the front ; sometimes regularly 

 arched from beak to front, and often arcuate in the upper part and straight in 

 the lower portion. Umbo prominent and much elevated above the hinge-line ; 

 beak more or less incurved over the fissure of the high and arcuate area, which 

 has a length of one-half to nearly two-thirds the width of the shell. Mesial 

 sinus wide and deep, sub-angular in the lower portion. 



Dorsal valve regularly arcuate ; the greatest convexity near the middle, and 

 regularly curving to the lateral margin ; mesial fold prominent, sometimes 

 rounded, but usually more or less distinctly angular ; beak small, slightly 

 incurved over a nearly vertical narrow area. Surface marked by from six to 

 ten more or less rounded, simple plications on each side of the mesial fold or 

 sinus, while there are three or four distinctly bifurcating or dichotomous plica- 



