DESCRIPTION OP SPECIES 317 



GENUS CLORINDA BARRANDE 



Clorinda transversa n. sp. 

 Plate 16, Figures 2 and 3 



Description : Shell transversely subelliptical in outline ; a little wider 

 than long; hinge line shorter than the greatest width, which is near the 

 middle of the shell ; front margin slightly extended. Specimens of nearly 

 average size have a length of % to ^4 inch, a width of % to % inch, and 

 a thickness of % to % inch. 



Ventral valve arched from beak to front; depressed along the median 

 portion in a rather broad mesial sinus, which extends from the beak to 

 the front margin; on each side of the sinus the curvature is rather abrupt 

 to the lateral and cardinal margins; the beak is pointed, elevated, and 

 strongly incurved; the cardinal area rather high, concave; spondylium 

 rather deep, supported by a high, slender median septum. 



Dorsal valve much less arcuate than the ventral, its greatest convexity 

 in the umbonal region ; the surface moderately convex from beak to front 

 and elevated into a prominent mesial fold, which becomes rather broad 

 in the anterior portion of the shell, where it is bounded by a poorly de- 

 fined depression ; antero-lateral portions nearly flat, postero-lateral slopes 

 rather gentle; beak pointed and strongly incurved beneath that of the 

 opposite valve. 



Surface of both valves nearly smooth, marked only by a few concentric 

 lines of growth, which are more numerous toward the outer margin of 

 the valves. 



Horizon and locality : Associated with Triplecia aff . insularis in a zone 

 about 18 feet above the base of the Kankakee limestone at Grafton, 

 Illinois. 



GENUS STRICKLANDINIA BILLINGS 



StricManclinia pyriformis n. sp. 

 Plate 16, Figures 8 and 9 



Description : The shell is subovate to pyriform in uutline ; the greatest 

 width below the middle ; the anterior margin somewhat extended ; lounded 

 or sometimes with a slight emargination on each side of the middle. The 

 valves are subequally convex; hinge line straight, from yj to j4 the 

 greatest width; the cardino-lateral angle about 90°. 



Ventral valve rather regularly convex along the median line from beak 

 to front, the greatest convexity a little posterior to the middle ; without 

 a distinct fold or sinus; the curvature rather gentle toward the antero- 

 lateral margins, but steep in the postero-lateral regions, where the valve 



