182 Twenty-fourth Report on tee State Musevm. 



^ 



gently convex on each side ; the length and width about as two to 

 three ; area about one quarter as wide as that of the ventral valve. 

 Yentral valve depressed-pyramidal, the apex projecting backwards 

 over the area ; the elevation about equal to half the length of the 

 dorsal valve ; area twice as wide as high ; fissure narrow, sides 

 nearly parallel and extending to the apex. 



Surface marked by strong angular strise which are increased by 

 interstitial additions to the number of twenty-eight or thirty on the 

 margin of the shell : striae crossed by distinct lamellose lines of 

 growth. 



Length five lines on the dorsal valve ; width seven lines. 



This species is of the type of 0, tricenaria, but the beak is much 

 more elevated, the area higher, and the strise more angular, and are 

 increased by interstitial additions, while in 0. tricenaria, and its 

 congener 0. peGtinella^ the strige are simple. 



Formation and locality. In beds of the Niagara group, near 

 Louisville, Ky. Cabinet of Dr. James Knapp. 



Orthis eug^plicata n. sp. 



Shell small, subquadrate, four-fifths as long as wide, gibbous, car- 

 dinal line nearly equal to the greatest width of the shell, angles 

 obtuse, basal margin nearly straight. Dorsal valve convex, with a 

 distinct median sinus extending from beak to base ; area of valve 

 linear. Length three lines, width four lines. Yentral valve depressed- 

 pyramidal, marked along the center by a. distinct angular plication 

 or fold ; beak pointed and 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 increased 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. In beds of the age of the Niagara group, 

 near Louisville, Ky. Cabinet of Dr. James Knapp. 



Spieifera eostellum n. sp. 



Shell rather below the medium size, somewhat subtriangular, with 

 a long, projecting ventral beak, which is abruptly incurved at the 

 extremity. Dorsal valve broadly elliptical, moderately ventricose, two- 

 thirds as long as wide, with a proportionally broad, elevated or rounded 

 mesial fold ; three plications mark the valve on each side of the 

 fold, the inner two originating as one at the apex and dividing below ; 



