154 THE DEVONIAN OF MISSOURI. 



Hinge line straight, length a little less than the length of the shell measured from 

 the anterior side of the beak to the extremity of the wing. 



Beaks anterior, acute, prominent, inclined forward. Umbonal region gibbous above, 

 regularly convex below, subtending an acute angle. 



Ear bending downward, with a strong fold in the upper part, limited by a broad 

 undefined sulcus and shallow byssal sinus. Wing triangular, flat, defined by the abrupt 

 retral bending of the striae and a depressed line along the post-cardinal slope; margin 

 concave; extremity acute. 



Test thin, marked by fine regular concentric striae, which at unequal intervals are 

 crowded into fascicles, giving an undulated aspect to the surface of the cast; in old 

 specimens, more crowded on the anterior side and ear, and on the wing usually regular, 

 sometimes becoming a little fasciculate on the margin." 



"Ligamental area narrow, marked by fine striae; below this area is a narrow oblique 

 fold or lateral tooth." 



Remarks — Only two identifiable specimens have been collected. The surface 

 markings are not well preserved and the reference might, with equal propriety; be to 

 L. bigsbyi Hall. 



Occurrence — Grand Tower limestone of Little Saline Creek. 



Genus Limoptera Hall 



Limoptera macroplera? (Conrad) 



Plate 36, figures 3 and 4. 



1838. Lima macroplera Conrad, Ann. Report N. Y. Geol. Surv., p. 117. 

 1884. Limoptera macroplera Hall, Pal. New York, vol. V, pt. 1, Lamellibranchiata, I, 

 pp. 246-248, pi. 24, fig. 14; pi. 26, figs. 6-9; pi. 27, figs. 1-10; pi. 28, figs. 4, 5; 

 pi. 29, figs. 1-4; pi. 92, figs. 4-9. 

 1909. Limoptera macroptera Grabau and Shimer, North American Index Fossils, I, 

 p. 422, fig. 553, d. 



Hall's description — "Shell large; including the cardinal expansions, the form is 

 subquadrate; body broadly ovate, erect or moderately oblique; wing more or less ex- 

 panded; height one-fourth to one-third greater than the length; basal margin broadly 

 rounded, with the anterior and posterior sides sub-parallel. 



Valves very unequal. Left valve ranging from moderately convex to very gibbous, 

 often somewhat regularly arcuate from beak to base. Right valve smaller than the 

 opposite, in young specimens nearly flat below, depressed-convex in the middle, and 

 more convex in the umbonal region; in specimens of medium size there is often a greater 

 convexity in the upper part and in very old specimens the surface is depressed-convex 

 and nearly flat in the lower part. 



Hinge line straight, sometimes equalling but usually less than the length of the 

 shell. 



Beak of the left valve prominent, acute, inclined forward, rising above and arching 

 over the cardinal line, situated anterior to the middle of the body of the shell. Umbonal 

 region prominent, convex in young shells and gibbous in older ones, limited anteriorly 

 by a distinct sulcus, and posteriorlyJpy the abrupt umbonal slope. Beak of right valve 

 acute, scarcely rising above the hinge line, defined anteriorly by the byssal sulcus, and 

 posteriorly by the abrupt depression and distinct limitation of the wing. Umbonal 

 angle acute. 



Ear small, well-defined in young specimens, and scarcely increasing in size in propor- 

 tion to the growth of the shells, limited by a distinct byssal depression; extremity 

 rounded. Wing large, triangular; margin more or less concave in young shells, and often 

 nearly straight in older shells; extremity produced or rectangular, often extending beyond 

 the posterior margin of the valve. 



