78 PALEONTOLOGY OF KENTUCKY. 



Rhynchonella pisa. HALL AND WHITFIKLD. 



Plate XXXII., figures 24 to 27. 

 Rhynchonella pisa, H. and W. Pal. of Ohio, Vol. II., p. 1351875. 



Shell small, globular in full-grown specimens, but varying from depressed 

 lenticular to highly gibbous at different stages of growth. Gfeneral outline of 

 the shell broadly ovate, widest near the front or below the middle of the 

 length. Ventral valve less gibbous than the dorsal ; beak small, pointed and 

 slightly curved, usually projecting but moderately beyond that of the opposite 

 valve, though sometimes rather extended ; body and sides of the valves regu- 

 larly rounded, becoming broadly but not deeply sinuate in front, where it is 

 prolonged and bent upward in the middle. Dorsal valve regularly convex, 

 center of the valve most prominent, becoming slightly elevated in front, form- 

 ing a not very prominent mesial elevation. Surface marked by from twelve to 

 sixteen rounded plications, which are distinctly marked on sides and in front, 

 but becoming obsolete soon after reaching the middle of the valve on the dorsal 

 side, but are continued somewhat further on the ventral valve, and in some 

 specimens those bordering the sinus extend to near the beak. On the dorsal 

 valve there are usually four plications elevated to form the mesial fold, and 

 three depressed in the ventral sinus, though in some cases there are only three 

 elevated on the dorsal valve. This species resembles Rhyn. neglecta, with 

 which it is associated, but differs in its general convexity of the valves and 

 want of angularity in the plications, which do not extend to the beak as in 

 that species. The more elongate forms have some similarity to Rhyn. acinus, 

 but have not the flattening of the sides and surfaces of the valves, as in that 

 species, and have, moreover, a greater number of plications. The more ventri- 

 cose forms resemble, very closely, small specimens of Rhyn. nucleolata, but, 

 besides being more elongate, with a more projecting beak, the plications are 

 never flattened on their surfaces, and .are destitute of the groove along the 

 middle, as in that one. (Hall and Whitfield.) 



Formation and Locality. Occurs in the Niagara rocks of the quarries east of the city of Louis- 

 ville. It is a rather rare species. The specimen illustrated on plate u 32 is of about the largest size this 

 species ever attains. 



Rhynchonella rugaecosta. K. sr. 



Plate XXXII., figures 48, 49, 50 and 51. 



Shell of medium size, sub-triangular or sub-pentagonal ; compressed or very 

 moderately convex ; width to length as three to two. 



Ventral valve moderately convex in the umbonal region, sloping from there 

 in a straight line to the baso -lateral margins, but rapidly, almost abruptly, to 



