LOWER HELDERBERG GROUP. 157 



Surface marked by closely arranged subequal concentric striae, and, when 

 exfoliated, by fine longitudinal striae, which are likewise conspicuous 

 upon the inner side of the shell. Substance of the shell closely lamellose. 

 This species is distinguished by its straight parallel sides and abruptly rounded 



base, with sloping cardinal margins, prominent beak, and extremely convex upper 



central portions of the shell. The striae are not conspicuously different from those 



of some other species of Lingula. 



Fig. 6. An individual of medium size. 



Fig. 8. A large individual of the same species. 



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

 group : Helderberg, Schoharie, Hudson, etc. 



Linpila spathata ( n. s.). 



Plate IX. Fia. 9, 7 & 11. 



Shell oval-ovate, with the sides scarcely curved and gradually converging 

 towards the cardinal extremity, which is obtuse : base abruptly 

 rounded or sub truncate. 



Surface marked by concentric lines of growth : vascular impressions 

 strongly marked upon the cast. 



This shell differs somewhat in form from L. centrilineata; and the aspect of the 

 shell, the interior markings, etc. present well-marked differences : the sides are 

 more nearly parallel, and the base less curved and more abruptly, sloping towards 

 the beaks. 



The specimen represented in figs. 7 and 11 presents many characters in common 

 with fig. 9, but it has a broader depression down the centre of both valves, which 

 are likewise more convex, and the longitudinal striae are more distinctly diverging 

 or radiating than in that one. In the imperfect condition of the specimens, it seems 

 more judicious to consider these as varieties of one species, than as distinct species. 



Fig. 9. A large individual having the upper part of the shell broken oflF. 

 Fig. 7 & 11. Two views of a specimen having the base broken off. The convexity of th« 

 two valves is more than one-third the greatest width of the shell. 

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

 group : Helderberg mountains and Schoharie. 



