6 



unknown in any species of Lunulicardium it is referred to the 

 genus, but it approaches nearer to it in external appearance than 

 to any other genus. . 



Found by R. A. Blair in rocks of the age of the Hamilton 

 Group at Providence, Missouri, and now in the collection of S. A. 

 Miller. 



LUNULICARDIUM RETRORSUM, n. sp. 



Plate II, Fig. 26, right valve of large specimen; Fig. 27, left 

 valve of small specimen; Fig. 28, cardinal view of same. 



Shell small, obliquely subovate. Valve highly convex. Height 

 about one- fourth more than the length. Anterior side recurved 

 and merged into the basal margin. Posterior margin somewhat 

 truncated and then gently rounded to the post basal extremity. 

 Basal margin abruptly rounded at the post basal margin. Beaks 

 near the middle, very prominent and incurved over the hinge line. 

 Umbones gibbous and gradually merged into the general convexity 

 of the valves. Thickness or width through the greatest convexity 

 of the valves equal to the length. Surface marked by sixty or 

 seventy fine radiating plications that increase by implantation in 

 the umbonal region. There are also undefined concentric undula- 

 tions of growth of the shells preserved on the casts. Our speci- 

 mens are casts quite well preserved. 



This species is distinguished by the great convexity of the 

 valves, prominent incurving beaks and retrorse or recurved ante- 

 rior margin. 



Found by R. A. Blair in the Chouteau limestones, near Sedalia, 

 Missouri, and now in the collection of S. A. Miller. 



blairella, n. gen. 

 Shell equivalve, inequilateral, elliptical, subovate or subcircular. 

 Margins closed. Beaks anterior to the middle and incurved. Um- 

 bones high and merging into the general convexity of the shell 

 below. Cardinal line straight posterior to the beaks. Ligament 

 external and contained in a groove along the cardinal line. No 

 cincture on the sides of the values. Surface marked by concentric 

 undulations or concentric lines of growth. There is a concave 

 pit beneath the beak of the right valve, anterior to which there is 

 a single tooth and posterior to which there is a strong bifid tooth. 

 Muscular impressions and pallial line not observed. Type B. 

 sedaliensis. 



