346 PALJBONTOLOGY OF NEW-YORK. 



Fig. 5 & 6. Interior of a small and a large rentral valve. 

 Fig. 7. The ventral valve enlarged. 



Geological position a?id locality. In the shaly limestone of the Lower Ilelderberg 

 group : Helderberg mountains; Catskill, Hudson, Schoharie, and other places. 



Leptocoplia inibricata. 



Plate XXXVIII. Fig. 8 - 13. 

 Shell longitudinally semielliptical or suborbicular. Ventral valve convex, 

 most prominent along the middle, and sloping laterally : beak small, 

 incurved at the apex and perforated by a very small round aperture, 

 one side of which is formed by the deltidium. Dorsal valve flattened 

 or depressed convex : beak scarcely elevated above the hinge ; hinge 

 line sloping from the beaks at an angle of about 150°, rounded at the 

 extremities, nearly equal to the greatest width of the shell ; false area 

 narrow, much shorter than the hinge. 

 Surface marked by ten to twelve plications on each valve, of which two 

 on the middle of the ventral valve are larger and more elevated than 

 the others, and separated by a wider and deeper depression than be- 

 tween those on each side. The central plication on the dorsal valve 

 is larger than the others near the front, but usually dies out before 

 reaching the beak. Shell marked by strong imbricating concentric 

 lamellae of growth. 



This species resembles Leptoccelia i^Atrypa) disparilis of the Niagara groujj, but 

 is generally larger, has more plications and a straighter hinge : its dorsal valve also 

 differs, in being slightly convex instead of concave. It also bears a general resem- 

 blance to Terebratula lepida (Goldfuss) and T. sublepida (de Verneuil), but has a 

 wider hinge than either of these, and differs likewise from them in other obvious 

 and essential characters. 



Fig. 8, 9 & 10. Illustrations of the dorsal and ventral valves of the ordinary forms of this 



species. 

 Fig. 11 & 12. Individuals differing somewhat in the plications from the more common forms. 

 Fig. 13. Dorsal view of a specimen enlarged. 



The comparative extension of the hinge line in different individuals is subject 

 to much variation. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Helderberg mountains; Schoharie, and other places. 



