HUDSON-RIVER GKOtJPi 287 



Fig. 2 d. A portion of the surface of one of these enlarged, showing the striato- punctate character. 

 Fig. 2 e. A cast of a large symmetrical specimen, showing the same characters of the surface, form of 



visceral impression, etc. 

 Fig. 2 / The impression made by the outside of the convex valve of this species, showing the fascicles 



of strias in a perfect manner. Specimens like this and the preceding are often found in 



connection, giving the impressions made by the two sides of the valve. 

 Fig. 2 g. A small specimen, preserving the shell, and showing the strisB in interrupted fascicles. 

 Fig. 2 ^t- A portion of the surface enlarged. 

 Figs. 2 A, t. Figures of specimens which still preserve a part of the shell, having the striae in broad 



fascicles of small ones separated by larger ones. 

 Fig, 2 k. Interior of the concave valve, showing the two small teeth on the hinge line, with three 



diverging callosities. 

 Fig. 2 I. Mould of the interior of the flat valve, showing, the two cavities made by the teeth, and the 



impressions of the radiating callosities. 



« 

 The general aspect of this species, as it occurs in the shaly and arenaceous strata of this 

 group, is more nearly like the same in the Blue limestone of Ohio and other western 

 localities, where there is a considerable admixture of argillaceous matter in the mass. In 

 both the Hudson-river group of New-York, and the western extension of the same strata, 

 where there are frequent alternations of shaly, arenaceous and calcareous matter, there is 

 a greater variety in form and appearance of the fossils. This species, therefore, in the 

 numerous localities within this State, presents much diversity of appearance, depending 

 upon the character of the rock, or upon the partial preservation of the shell. 



Position and locality. The most prolific localities of this species in this group are Pulaski, 

 and Washingtonville, in Oswego county ; near Rome, Oneida county ; near Boonville, 

 Turin, and Martinsburgh, in Lewis county. It is equally abundant in numerous localities 

 on the north side of Lake Ontario. (State Collection.) 



146. 9. LEPT^NA SERICEA. 



Pi.. LXXIX. Figs. 3 a, b. 

 Reference pag. 110, pi. 31 b, or this volume. 



This species is often quite abundant in the rocks of this group, extending almost to its 

 highest limit. The shell is usually removed, and specimens are found mostly in the form of 

 moulds or impressions of the shell. In some localities, when well preserved, the alternating 

 stronger striae are more distinct than in those of the Trenton limestone. 



Fig. 3 a. A mould of the interior of the shell. 



Fig. 3 b. An enlarged portion, showing the striato-punctate character of the surfaca 



Position and locality. This species is found in all the localities with the preceding, and 

 rarely in the Ulica slate. (State Collection.) 



