Contributions to Invertebrate Palaeontology. 557 



V 



Genus ACTIXODESMA Sandb. 



Actiiiodesiua subrecta. 



Plate XI, fig. 20. 



Actinodesma subrecta Whitf., Ann. N. Y. Acad. Sci., 1882, p. 215. 



Shell of moderate size; the body of the shell, exclusive of the wings and 

 hinge extensions, ovate in outline, and slightly oblique to the cardinal line. 

 Hinge-line extended in the form of strong auriculations or wings on the sides 

 of the shell, the upper margin straight, or a little declining on each side of 

 the beak ; anterior wing short, triangular and divided from the body of the 

 shell by a deep and wide sub-triangular notch ; posterior side long and sub- 

 mucronate at the extremity, three to three and a half times as long as the 

 anterior side, and its area much greater, extending along the body of the 

 valve to nearly half its length from the beak. Body of the left valve more than 

 moderately convex, and strongly arcuate or bent between the beak and base 

 of the shell ; so that when placed on a flat surface, the margin, especially on 

 the posterior side, would be much elevated above the plane. Beak of the 

 valve large, sub-tumid, and slightly extended above the cardinal line. Length 

 of the body of the shell, from the cardinal line to the base, about one-fiftli 

 greater than across it in the opposite direction. Anterior border broadly 

 ronnded,the basal margin more sharply so, with a slight angularity at its 

 junction with the nearly direct posterior border. Surface of the shell marked 

 by irregular, concentric, strongly lamellose lines, resembling those of the oyster. 

 Right valve not yet observed from Ohio. 



The species is allied to A. recta — Avicula recta Conrad, but is 

 shorter, more ventrieose on the left side, more arcuate or bent, and 

 with less extended wing's. It is not an uncommon species in the 

 soft shales of the Hamilton group of New York, where it is readily 

 recognized from A. recta by the above-mentioned characters. The 

 A. recta is most common in the arenaceous beds of eastern New 

 York, while this is the prevailing form among the soft shales fur- 

 ther west. The right valve is there recognized as being shorter 

 than the left, concave instead of convex, with aa appressed beak or 

 umbo not extending beyond the cardinal line, and the valve is much 

 thinner in its substance. 



Formation and Locality. — In layers of brownish limestone above 

 the " Bone-bed," at Fishinger's mill, Franklin Co., Ohio. Collected 

 by the Hyatt brothers, of the State University at Columbus. 



