80 PALEONTOLOGY OF KENTUCKY. 



lar bend, in the dorsal direction. The number of depressed plications is very 

 variable, running from three to nine ; the deflected front part of the valve is 

 quadrilateral, its length sometimes exceeding its width ; its deflection amounts, 

 usually, to ninety degrees, but it sometimes exceeds the right-angle a few 

 degrees. 



The dorsal valve is very gibbous, having its greatest convexity a little below 

 the middle of the valve, from where it curves regularly and gently to the front 

 and rear, but very abruptly to the lateral margins ; there is a slight depression 

 in the middle of the valve from apex almost half-way down or even a little 

 further. Where this depression terminates some of the central plications, 

 from five to ten in number, commence to rise, increasing in elevation towards 

 the front, forming here a kind of mesial elevation. This valve has in its front 

 part a quadrilateral indentation, corresponding in form and size to the front 

 extension of the ventral valve, which fits into it exactly. The base of the 

 shell forms a regular quadrangle. The surface is covered by fine radiating 

 plications, rounded or somewhat flattened, some of which bifurcate ; they 

 differ in size and number, which latter runs from twenty to thirty. Two some- 

 what different forms of this species are found, as represented by the figures in 

 the two different plates ; the group represented on plate 27 is somewhat longer 

 than wide, and its plications are less in number, and markedly coarser, while 

 the shells figured on plate 33, are wider than long, with finer and more numer- 

 ous plications; but there are so many specimens of intermediate forms con- 

 necting the two groups, that I feel not justified to separate them as different 

 species or varieties. 



This species differs greatly in size in different specimens ; one of average size 

 has the following dimensions : width, seven lines ; length, eight lines, and 

 thickness, from six to seven lines. 



Formation and Locality. Occurs somewhat abundantly in the Niagara rocks in the quarries east 

 of the city of Louisville, Ky., where even well preserved specimens are not rare. This species was 

 named by Prof. Hall after Prof. Safford, of Nashville, Tennessee, formerly State Geologist of Tennessee. 



Rhynchonella saffordi var. depressa. K. VAR. 



. Plate XXXIII., figures 1, 2 and 3. 



Although this shell agrees in so many points with Rhyn. saffordi, to place it 

 with that species, it, on the other hand, possesses some very important features 

 which separate it from saffordi, and which I think justify me to make a new 

 variety out of it. These features are as follows : 



1. This shell is very flat or compressed, more so than any other Rhyncho- 

 nella of its size, while Rhyn. saffordi is generally very ventricose. 



