LOWER HELDERBERG ROCKS. 
331 
Fig. 1 a , b , The anterior and posterior sides of a small specimen. 
Fig. 1 c. Enlargement of the surface, showing the undulating transverse lamellae and the 
fine longitudinal striae. 
Fig. 2 a, b. Views of the anterior and posterior sides of a larger individual. 
Fig. 3. A larger individual, in which the transverse lamellae are much subdued : the lon¬ 
gitudinal ridge is an accidental feature. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Helderberg mountains, Albany county. 
Platyceras spirale (n. s.). 
Plate LXIII. Fig. 4, 5, 6, 7, 8, 9. 
Shell spirally ascending : apex consisting of a single minute closd 
volution, below which are one or two widely separated and gradually 
enlarging volutions : aperture spreading, rounded or broad oval; peri¬ 
stome sinuate. 
Apex and upper part of the shell smooth, or with only fine transverse 
striae, more or less distinctly plicated on one side below, with strong 
lamellose undulating striae. 
This species presents considerable variation during its different stages of growth; 
and in the degree of development of the plications; but there seems to be no real 
specific distinction among the specimens examined. 
Fig. 4. A young individual of this species, in which no plications are developed. 
Fig. 5 a. A larger specimen, in which the plications are very strongly developed on the 
right posterior side of the shell. 
Fig. 5 b. The posterior side of the same shell. 
Fig. 6. A specimen of equal size with the preceding, in which the plications are but par¬ 
tially developed, or shown principally in the undulations of the striae of the 
surface. 
Fig. 7. A similar specimen which is smooth on the anterior side, and showing only two or 
thrfee plications on the posterior side. 
Fig. 8. A more elongated specimen, with strongly developed plications. (The upper part has 
been broken off, and presents some imperfection at the junction of the two parts.) 
Fig. 9 a. The anterior side of another specimen, in which plications are but faintly developed. 
Fig. 9 b. The posterior side of the same. The expansion towards the aperture is increased 
beyond the natural width, by compression. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group Albany and Schoharie counties. 
