PALAEONTOLOGY OF IOWA. 717 



SURFACE marked by fine concentric striae and some stronger 

 lines of growth. Hinge-line marked, on the posterior side of 

 the beak, by thirteen or fourteen small prominent teeth, 

 which increase in strength as they recede from the beak ; 

 anterior side with several small teeth, and two others much 

 stronger with a deep pit between : muscular impressions 

 strongly marked ; shell thickened just within the margin. 



Fig. 4. View of the interior of a left valve. 

 Fig. 5 a. Exterior of the left valve of another individual. 

 Fig. 5 b. Cardinal view of the same. 

 Geological formation. In the Coal measures. 



Leda bellastriata. 



PLATE XXIX. FIG. 6 a. b, c, d. 

 Leda bellastriata : STEVENS, Am. Journal of Science, Vol. xxv, p. 261. 



SHELL about twice as long as wide, broadly subovoid an- 

 teriorly, contracted and attenuated posteriorly, gibbous on 

 the umbones : beaks anterior to the centre of the shell, much 

 elevated, sharp, incurved, appressed at their extremities, and 

 pointing posteriorly : hinge-line curved, armed with about 

 eleven or twelve teeth on the anterior side of the beak, with 

 about an equal number on the posterior side. Externally the 

 cardinal line on the posterior side is sharply elevated, with 

 a space between it and the umbonial slope, which is flat or 

 slightly concave ; the escutcheon faintly defined, long and 

 narrow. 



SURFACE marked by fine abruptly elevated concentric 

 strise, which become obsolete in passing over the posterior 

 slope, and strong on the flattened area adjacent to the cardi- 

 nal line. 



This shell differs from Leda (JVwcuZa) arata ( HALL in STANSBURY'S Report), in 

 having the heaks more abruptly elevated, the escutcheon less strongly marked, and 

 the concentric strise much finer. 



Fig. 6 a. View of the right valve of a small individual, which is imperfect at the 



posterior extremity. 

 Fig. 6 b. Cardinal view of the same. 

 Fig. 6 c. Interior of the right valve of a larger individual, in which the teeth are 



broken off on the posterior side. 

 Fig. 6 d. Enlargement of the concentric strise. 



Geological formation and locality. Lower Coal measures : Illinois. 



