a 20 
PALAEONTOLOGY OF NEW-YORK. 
Fig. 8 
a. 
Fig. 8 
b. 
Fig. 8 
c. 
Fig. 9 
a. 
Fig. 9 
b. 
Yiew of the aperture and lower side of the shell (which is represented as too 
smooth in the figure, from a little adhering stone). 
Yiew of the spire and upper side of the volutions, showing the folds or carina. 
An oblique view, showing the sinuosity in the anterior margin of the aperture. 
An older specimen in which the inequalities from the upper part of the last volu¬ 
tion are worn off, the plications being more strongly marked on the peristome. 
Dorsal or profile view, showing the outer volution above the apex of the spire. 
The deep sinus in the anterior margin of the younger shell is not conspicuous in 
this one, the peristome having become strongly and almost regularly plicate, 
except on the posterior side, where there is a broad shallow sinus. 
Geological position and locality. In the slialy limestone of the Lower Helderberg 
group : Albany and Schoharie counties. 
Plat} ceras rctrorsum (n. s.). 
Plate LVIII. Fig. 10 a b, & 6 c; and Plate LIX. Fig. 9 a, b. 
Shell spiral; the apex above, or on the same plane with the outer volu¬ 
tion : volutions about two, the first one nearly smooth, gradually 
becoming spirally angulate or plicate upon the surface; upper side 
flattened, the lower side rounded : aperture somewhat round; peri¬ 
stome sinuate. 
Surface marked by fine crowded transverse striae which are extremely 
sinuate, the sinuosities varying at different stages of growth, crossed 
by fine revolving striae. 
This species resembles the preceding in some respects; but in three specimens 
examined, the volutions are free, the shell a little more robust, and some of the 
angles more sharply defined. One specimen, which may be a variety of the same 
species, is less angular, more extended on the umbilical side, and has the apex of 
the spire below the plane of the outer volution. 
Fig. 10 a. The upper side of the spire, from which the shell is worn smooth and partially 
removed. 
Fig. 10 b. Profile view, showing the dorsal side and the elevated apex of the spire. 
Fig. 6 c. An imperfect specimen, which may be the young of the same. 
Plate LIX. Fig. 9 a, b. A specimen which is probably of this species. The specimen figured 
is broken at the apex, and somewhat otherwise distorted. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
mountains : Albany and Schoharie counties. 
