PALEONTOLOGY OF NEW-YORK. 
sometimes slightly concave, is never so distinctly impressed as it often is in species 
of the type of R. wilsoni. 
Fig. 2 a, b. Dorsal views of two small individuals. 
Fig. 2 c, d. Front views of the same. 
Fig. 2 e. Profile of one of these. 
Fig. 2 f, g. Dorsal and ventral views of a larger individual. 
Fig. 2 h, i. Front and profile of the same. 
Fig. 2 k. Enlargement of the surface, showing the angular plications and sharply arching 
striae, 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. 
Rhynchonella acutiplicata (n. s.). 
Plate XXXIII. Fig. 3 a - e . 
Shell subquadrangular, compressed. Yentral 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. 
Surface 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 
subimbripating concentric lines of growth. 
A distinguishing feature of this species is the sharply angular or subcarinate 
plications : in this character, however, it approaches 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. 
o 7 
Fig. 2 e ( by mistake 3 cl). Enlargement of the plications and concentric strim. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Schoharie. 
