514 Contributions to Invertebrate Palaeontology. 



and in the deeply divided feature of the cast of this valve. The 

 dorsal valve is much less marked, and is often destitute of any dis- 

 tinguishing feature. 



Formation and Locality. — In the hydraulic limestone of the 

 Lower Helderberg group, in Adams County, Ohio, occurring in 

 numbers densely packed together, but having the shelh^ substance 

 entirely removed. 



MOLLUSCA. 



LAMELLIBRANCHIATA. 



Genus PTERI\EA Goldfuss. 



Pteriiiea aviculoidea. 



Plate V, fig. 23. 



Megamhonia aviculoidea Hall, Pal. N. Y., vol. 3, p. 274, ^il. 49, figs. 7 and 8. 

 Pterinea aviculoidea (Hall) Whitf., Geol. Kept. Wis., vol. iv, p. 322, pi. 25, figs. 

 6-7. 



Shell of proportionally small size, obliquely rhomboidal in outline, -with a 

 moderately long, straight hinge-line, but little shorter than the length of the 

 body of the shell below. Left valve depressed convex, with a small, slightly 

 incurved beak, scarcely extending above the cardinal line. Anterior end 

 short, and the anterior projection scarcely defined ; posterior wing concave 

 and the posterior margin nearly at right angles to the hinge-line for a short 

 distance below, then gently curving backward to the rounded postero-basal 

 extremity ; basal line rounded and on the anterior side of the umbonal ridge 

 curving rapidly upward to the anterior exti'emity. Body of the valve convex 

 and oblique to the hinge, the umbonal ridge broadly rounded. Surface of the 

 shell marked only by lines of growth some of which are stronger and form 

 slight varices. 



The species is poorly represented in individuals, but the speci- 

 mens seen are so precisely like those of the Tentaculite limestones 

 of New^ York as to be not readily mistaken. 



Formation and Locality. — In the hydraulic limestone of the 

 Lower Helderberg group on Put-in-Ba}^ Island, Lake Erie. 



• 



Genus GOIVIOPIIORA Phillips. 



Goniopliora dubia. 



Plate V, figs. 24^26. 

 Modiolopsis? dubius Hall, Pal. N. Y., vol. 3, p. 2G4, pi. 49, fig. 2. 



Shell small, transversely elongate, nearly twice and a half as long as high. 

 Valves ventricose, most highly convex on the anterior half, becoming more 

 depressed toward the posterior ; beaks small, very slightly incurved but not 



