334 Thirty-fifth Report on the State Museum. 



sulcus, and on the posterior side sloping abruptly to the wing. 

 Anterior wing short, denned by a deep sulcus and a marked byssal 

 sinus. Posterior wing large, depressed- convex, much extended, 

 joining the body of the shell below the middle, and defined only by 

 the recurving of the striae; margin concave; extremity acute. 



Test thick, marked by numerous fine striae of growth, which at 

 intervals are crowded into fascicles, producing an undulating sur- 

 face. The striae are more closely arranged, and become lamellose 

 on the anterior part of the shell. On the posterior wing the striae 

 are regular, and at distant intervals a single striae becomes sharply 

 elevated. 



The specimen of this species described has a length 60 mm., 

 height 66 mm., and hinge-line equal to, or greater than, the length 

 of the shell. 



This species resembles G. erectum, but appears to be a more robust 

 form ; the shell is more orbicular, the umbonal region more gibbous, 

 the surface more rugose from the undulations of the fascicles of striae, 

 and the limitation between the body and the posterior wing is less 

 strongly defined. 



Formation and localities. In the limestone of the Upper Helder- 

 berg group at the falls of the Ohio, near Louisville, Kentucky, and in 

 Clarke county, Indiana. 



LEIOPTERIA, Hall. 



Leiopteria l^vis. 



Ancula lewis, Hall. Geolog. Surv. N. Y. : Rep. Fourth Dist., p. 181. 1843. 

 Pteronites Icevis (Hall), S. A. Miller. Cat. Amer. Pal. Foss.,p. 202. 1877. 

 Leiopteria Icevis, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 

 17, figs. 5-11. Jan., 1883. 



Shell small, sub-rhomboidal ; body obliquely ovate ; length and height 

 nearly equal ; greatest length below the middle ; margins regularly 

 rounded, somewhat extended on the post-basal side. Left valve 

 more convex than the right ; the greatest convexity in both valves 

 is about the middle. Hinge-line straight on the posterior side of 

 the beak, turning abruptly downward in front ; entire length greater 

 than the length of the shell. Beaks obtuse, rounded, inclined for- 

 ward, situated at the anterior third of the shell, that of the left 

 valve quite prominent. Unibonal region of left valve prominent, 

 subtending an acute angle. Ear triangular, nearly equilateral, with 

 a strong angular fold along the middle, separated from the body of 



