LOWER HELDERBERG ROCKS. 
S37 
d of the same plate are given to illustrate this form. Fig. 3 and 4 a, 6, c, d , e,jf, of 
the - same plate, illustrate specimens with from two to four plications on the mesial 
elevation, and from four to six on each side. One specimen from the shaly limestone 
of Becraft’s mountain shows a single sharp plication in the mesial sinus, and two 
elevated upon the opposite valve. 
Fig. 6 a - e. Ventral, dorsal, profile, and front views of several individuals of the.typical 
form, with strong plications. 
Fig. 6 f - l. Specimens with finer and more numerous plications. 
Fig. 6 m - y. Illustrations of specimens which present the ordinary variations of full-grown 
individuals, from the Upper Pentamerus limestone. 
Geological 'position and locality. In the shaly limestone of the Lower Helderberg 
group, and in the Upper Pentamerus limestone : Helderberg mountains, Schoharie, 
Hudson, Catskill, Carlisle, Cherryvalley, and other places. 
Kliynchonella eininens (n. s.). 
Plate XXXVII. Fig. 3 & 4. 
Shell abruptly ovoid or depressed subg’lobose. Dorsal valve the larger, 
elevated near the front into a flattened mesial prominence, from which 
it declines gently towards the beak and more abruptly towards the 
lateral margins, which are deflected towards the opposite valve : beak 
incurved. Ventral valve flattened, very abruptly deflected at the mar¬ 
gins towards the opposite valve, having a broad well-defined sinus 
reaching from near the middle to the front, and prolonged into a lingui- 
form extension. 
Surface marked by about twenty-six rounded or scarcely subangular 
plications, about six of which are on the mesial fold and five in the 
opposite sinus; the whole crossed by fine undulating or zigzag lines of 
growth near the front of the valves. 
Sometimes the plications bounding each side of the mesial fold in this species 
bifurcate ; and one of them becomes obsolete before reaching the front, as in R. 
abrupta and R. vellicata. From both of these species, it may be distinguished by its 
more rounded plications and more prominent mesial fold, as well as in being a more 
robust shell. 
Fig. 3 a, b. Dorsal, front, and profile views of an individual of medium size. 
Fig. 4 a. Dorsal valve of a larger individual. 
The species sometimes attains larger size than fig. 4. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Helderberg mountains, Albany county. 
