NATURAL SCIENCES OF PHILADELPHIA. 457 



Genus SOLEMYA, Lamarck, 



Solemya radiata. Shell very thin, narrow, or elongate subelliptieal, 

 moderately convex ; ventral margin straight, or slightly concave along the 

 middle ; anterior (longer) side narrowly rounded at the extremity, the most 

 prominent part being a little above the middle ; posterior (shorter) side rather 

 narrowly rounded ; dorsal border nearly parallel to the base in front of the 

 beaks, and declining more rapidly, with a slightly concave outline behind 

 them. Surface with obscure concentric marks of growth, crossed by flat, 

 nearly obsolete, radiating plications, which are sometimes separated near the 

 middle of the valves, by spaces greater than their own breadth ; on the 

 anterior side, where they are very oblique, and more closely arranged, they 

 sometimes become irregular, and scarcely distinguishable from finer irregular 

 radiating strise; not well defined on other parts of the shell. 



Length 1-10 inch ; heighth 0*50 inch; convexity 0*36 inch. 



Locality and position. Grayville, Illinois. Coal measures. 



Genus LEDA, Schumaker. 



Leda (Yoldia ?) levistriata. Shell rather under medium size, narrow 

 subovate, moderately convex in the central and anterior regions, more 

 compressed posteriorly ; base forming a broad semiovate curve, the most 

 prominent part of which is a little in advance of the middle ; anterior side 

 rounded ; posterior side somewhat contracted, or narrower than the other, 

 and more abruptly rounded at the extremity, which is a little gaping ; dorsal 

 margin declining gently, and rather concave behind the beaks, nearly 

 horizontal and slightly convex in front of them ; beaks depressed and located 

 a little behind the middle ; surface apparently smooth, but when examined 

 by the aid of a good lens it is seen to be marked by extremely fine, obscure, 

 regularly arranged concentric strise. 



Length 0-57 inch ; heighth 0-20 inch ; convexity 0-14 inch. 



Locality and position. Waterloo, Monroe County, Illinois. Upper part of 

 St. Louis Limestone, of the Lower Carboniferous series, where it was found 

 associated with some of the small fossils described by Prof. Hall, from 

 Spurgeon Hill, Indiana. 



Genus SCHIZODUS, King. 



Schizodus Chesterensis. Shell rather large, transversely ovate, convex 

 in the anterior and umbonal regions, and cuneate posteriorly. Anterior 

 side regularly rounded ; base forming a broad, irregular, semiovate curve, 

 being usually slightly more prominent a little behind the middle than 

 elsewhere, thence nearly straight and ascending gradually to the posterior 

 extremity ; posterior side contracted, considerably longer than the other, and 

 abruptly rounded or subangular at the termination, the most salient part 

 being rather above the middle ; dorsal margin nearly straight and declining 

 gradually behind the beaks, from which it rounds regularly into the anterior 

 margin in front. Beaks gibbous, rather elevated, incurved, and located less 

 than one-third the length of the shell from the buccal margin. Muscular 

 impressions shallow ; those in front ovate, placed near the margin, and a little 

 above the middle ; those on the posterior side oval, and located near the 

 dorsal edge, about half-way between the beaks and the anal extremity. 

 Surface marked only by fine lines of growth. 



Length (of internal) l - 38 inches ; height 1 inch; convexity 0-78 inch. 



Resembles closely the Permian species Axinus obscurus, Sowerby, but is less 

 elevated in proportion to length, and has rather more oblique umbones ; while 

 the most salient part of its posterior margin is a little above, instead of below 

 the middle. It is usually found in the condition of internal casts. 



Locality and position. Chester, Illinois. Upper part of Chester Limestone, 

 of the Lower Carboniferous series. 



1860.J 



