PALAEONTOLOGY OF NEW-YORK. 
314 
in that one are more oblique, and never so nearly in the same plane, but the aper¬ 
ture is more nearly round, 
These differences are very perceptible in a comparison of the figures on Plates 
lv and lvi. The peculiarities of form may serve to distinguish the casts of the two 
species, while the undulating striae of the one under consideration will distinguish 
them by the surface characters. 
Fig. 10. View of the spire of a large individual, showing the undulating striae and the 
sinuosities of the right side of the aperture. 
Fig. 11 a. View of the aperture of a smaller specimen, which is a cast. 
Fig. 11 b. View of the aperture of a similar specimen. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Albany and Schoharie counties. 
Platyceras siimatiiiii (n. s.). 
Plate °LY. Fig. 5 & 7; and Plate LVII. Fig. 2. 
Shell depressed, somewhat obliquely ovoid : volutions about three, con¬ 
tiguous, the last one becoming very ventricose, a little flattened on the 
upper side, and expanded laterally to the axis of the spire : aperture 
broad campanulate ; margin deeply sinuate. 
Surface marked by fine concentric or transverse lamellose striae, and 
stronger wrinkles or folds. The striae are abruptly bent backwards on 
the upper dorsal side, and a deep sinus marks the labrum : the lower 
side of the aperture is likewise deeply sinuate. 
The specimen fig. 5 is vertically compressed on the outer margin of the last vo¬ 
lution and towards the aperture, leaving its inner margin a little elevated, and the 
inner volutions a little below the plane of the last volution. The other specimen, 
referred with doubt to this species, is distorted by pressure, and the upper volutions 
of the spire are a little above the plane of the outer volution. The sinuosity in the 
smaller specimen is wide and well defined : in the larger one it has, in the young 
state, been similar to the other, but has become a narrow slit towards the aperture. 
A similar change takes place in other species as they advance in age, till the notch 
is finally entirely closed. 
Fig. 5. View looking upon the spire of a small specimen, showing the deep marginal sinuo¬ 
sity and the strongly wrinkled surface. 
