LOWER HELDERBERG ROCKS. 
323 
becomes finely and obscurely plicate towards the aperture, and the left 
side marked with two or three coarse plications, while the transverse 
strise become more conspicuous and the longitudinal striae more subdued 
or obsolete. 
This species bears some resemblance to P. ventricosum ; but the last volution 
expands laterally much more rapidly, and is never so ventricose as in that species; 
while at the same time the obtusely angular form of the young shell, and the 
plicate margins of the older ones, sufficiently distinguish this species. 
Fig. 5 a , 6. Young specimens of this species. 
Fig. 5 c. A larger specimen, showing a shallow sinus on the back and the commencement 
of small plications on the right side. 
Fig. 5 d. A larger specimen where the plications are more fully developed. 
Fig. 5 e. Dorsal view of a similar specimen in which the plications are. more developed, and 
the obtuse carina extending from the apex is more defined, and ending in a broad 
extension in front (which is broken off in the specimen figured ). 
Fig. 5 f. View of the aperture of the same specimen, showing the incipient plications upon 
the left side of the aperture. This feature is much more strongly developed in 
some specimens than in this one. 
Fig. 5 g. A specimen in which the spiral carina is more strongly developed, and is marked 
by a deep sinuosity in the peristome. 
Fig. 5 h. An enlargement of the surface, showing the bending of the strise as they cross the 
carina. 
Fig. 5 i. An enlargement of the surface of a young specimen, where the longitudinal strise 
are more conspicuous. 
Fig. 6 c. This specimen is probably one of the same species, which is less expanded towards 
the aperture, and has one more volution at the apex than the preceding figures. 
Geological position and locality. In the middle portion of the shaly limestone : 
Base of Helderberg mountains, Albany county. 
Platyceras gibbosuin ( n. s.)» 
Plate LIX* Fig* 6 d - g, & 7 a, 
Shell obliquely subovoid, with one or two closely contiguous volutions at 
the apex, from which the last one expands more or less rapidly, be¬ 
coming ventricose in the middle and below; upper part of the last 
volution rounded, becoming angular and plicate below : aperture some¬ 
what rounded; peristome sinuous. 
