44 PALAEONTOLOGY OF KENTUCKY. 



group, from which it differs only in internal characters. It is also closely 

 allied to O. tulliensis, from which it can only be distinguished by characters of 

 the interior. 



Formation and Locality. Occurs in the upper strata of the Devonian formation, in Jefferson 

 county, Kentucky, and in Clark county, Indiana. Fair specimens are rather rare. 



Orthis rugaeplicata. HALL. 



Plate XXVII., figures 1, 2 and 3. 



Orthis rugaeplicatas, Hall. 24th Rep. N. Y. St. Mus., p. 1821872. 

 Orthis rugaeplicatas, Hall. 27th Rep. N. Y. St. Mus., pi. 9, figs. 1, 2 and 31875 



Shell small, subquadrate, four-fifths as long as wide, gibbous ; cardinal line 

 nearly equal to the greatest width of the shell ; cardinal angles obtuse, basal 

 margin nearly straight. Dorsal valve convex, with a distinct median sinus 

 extending from beak to base ; cardinal area linear ; length three lines, width 

 four lines. Ventral valve depressed-pyramidal, marked along the center by a 

 distinct angular plication or fold ; beak projecting slightly backwards over 

 the area ; area moderate, less than one- third as high as wide, and divided in 

 the center by a moderately wide fissure. 



Surface marked by very strong, sharply angular plications, which are in- 

 creased by interstitial additions, and of which there are about fifteen on the 

 margin of each valve, with a few other incipient ones. 



Formation and Locality. Found in the Niagara formation in the quarries east of the city of 

 Louisville, Ky. It is, when well preserved, an elegant little shell: but perfect, even fair specimens, are 

 very rare ; those of Dr. James Knapp, deceased, and my own, are all, so far found 



Orthis subnodosa. HALL. 



Orthis subnodosa, Hall. Trans. Alb. Inst., Yol. X. 1879. 

 Orthis subnodosa, Hall, llth Geol. Rep. of Ind., p. 2861881. 



It appears from Prof. Hall's description and illustration in the above men- 

 tioned report of Indiana, that he was then in possession of only the ventral 

 valve of this species, and the same is the case with me to-day.- Prof. Hall 

 describes this shell as follows : 



Ventral valve sub-orbicular, length and width about as ten to fourteen ; 

 hinge-line much shorter than the greatest width of the shell ; an undefined 

 mesial depression in the lower half of the shell. (In this last feature my 

 shell differs from Prof. Hall's, in having this depression extend all the way 

 up to the apex, but it is possible that this extended sinus was caused by 

 the breaking off of one of the adjacent ribs.) The umbo is comparatively 

 prominent ; beak small and slightly arched ; area small, triangular, apparently 



