939 PALEONTOLOGY OP NEW-YORK. 



sometimes slightly concave, is never so distinctly impressed as it uiten is in species 



of the type of R. vnlsoni. 



Fig. 2 a, b. Dorsal views of two small individuals. 



Fig. 2 r, d. Front views of the same. 



Fig. 2 e. Profile of one of these. 



Fig. 2y, g. Dorsal and ventral views of a larger individual. 



Fig. 2 A, I. Front and profile of the same. 



Fig. 2 k. Enlargement 6f the surface, showing the angular plications and sharply arching 

 stria;, which are more closely arranged than represented in the figure. 



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

 group : Albany and Schoharie counties. 



Rliynclionella acutiplicata ( n. s.). 



Plate XXXIII. Fiu. 3 a - e. 



Shell subquadrangular, compressed. Ventral valve depressed convex, most 

 prominent near the beak. Dorsal valve slightly larger than the ventral, 

 most prominent in the middle, declining with a gentle curve towards 

 the beak and margins : beak incurved. 



SuBFACE ornamented by about twenty-seven simple, moderately elevated, 

 acutely angular or subcarinate plications on each valve, about five of 

 which are elevated on the dorsal valve into a mesial prominence, which 

 dies out before reaching the beak, and widens rapidly towards the front. 

 On the ventral valve, four of the plications are depressed so as to form 

 a broad rather shallow mesial sinus, with sloping sides, extending about 

 two-thirds of the way to the beak. Shell marked by fine very regular 

 Bubimbricating concentric lines of growth. 

 A distinguishing feature of this species is the sharply angular or subcarinate 



plications : in this character, however, it ajiproaches the last described species; but 



its general form is much more compressed, proportionally more elongate, with more 



numerous and finer plications. 



Fig. 3 a, b. Dorsal and ventral views of a specimen of this species. 



Fig. 3 c, d. Profile and front views of the same. 



Fig. 2 « ( by mistake 3d). Enlargement of the plications and concentric striso. 



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

 groap : Schoharie. . 



