LOWER HELDERBERG ROCKS. 
319 
Platyceras pentalobus (n.s.). 
Plate LYIII. Fig. 7 a, b, c. 
Shell obliquely subconical : spiral with about two volutions; apex and 
upper volution smooth and rounded, becoming plicate on the last volu¬ 
tion ; plications four, five or more ; peristome simple. 
Surface marked by fine transverse striae, which are strongly undulated 
in passing over the plications. 
I have not been able to trace this species through its gradations of form; but it is 
so diiferent from the other species observed, that I can have no doubt of its specific 
distinctness. 
Fig. 7 a. View of the spire and the plications of the surface. 
Fig. 7 b. View of the aperture and lower part of the spire. 
Fig. 7 c. Profile or dorsal view. 
Geological position and locality. In the central portion of the Lower Helderberg 
group : Base of the Helderberg mountains, Albany county. 
Platyceras liiultismuatuin (n. s.). 
Plate LYIII. Fig. 8 a, b, c, & 9 a, b. 
Shell subdiscoid in the young state; apex nearly on a plane with the 
outer volution : volutions about three, the first ones minute; outer 
one becoming free, ventricose, rounded or scarcely angular below, 
somewhat flattened on the upper side, marked by several ridges and 
shallow depressions on the upper and dorsal side : aperture somewhat 
longitudinally oval; peristome sinuate, with a deeper sinuosity on the 
anterior margin. 
Surface marked by fine transverse striae, which are strongly undulated 
on the inequalities of the shell, and crossed by fine longitudinal or 
revolving striae. 
This is a very distinct and pretty species, which, in its younger condition, shows 
all the volutions contiguous; but as it advances, the outer one continues in a direct 
line, and, expanding more rapidly, the shell loses its subdiscoid character as in fig. 
9 a. The plications become more strongly developed and more numerous as the shell 
grows older : at the same time, by the increase of the outer volution, the apex of 
the spire becomes depressed below its plane. 
