LOWER HELDERBERG ROCKS. 
S73 
Leperditia alta. 
Plate LXXIX A. Fig. 6 a - e. 
Cytherina alta : Conrad. Vanuxem, Geological Report of the Fourth District, 1843, p. 112, f. C. 
Carapace subreniform : valves strongly convex, gibbous in the middle, 
somewhat variable in their proportions, straight above and broadly 
rounded below, the extremities obliquely rounded, the dorsal angles 
varying in their degree of development; posterior side broader than 
the anterior- : ventral margin of the right valve abruptly incurved, 
sometimes leaving an apparently obtuse carination along the line of 
bending. Anterior or eye tubercle distinct in the test, and sometimes 
distinct in the casts : not unfrequently there is a little inequality of 
surface between the anterior tubercle and the anterior dorsal angle. 
Central tubercle a gibbous area, not defined on the exterior surface, but 
from which, in casts and partial casts, the internal vessels are seen to 
radiate. 
The anterior edge often presents a slight marginal rim, but this is rarely 
seen on the posterior border of the specimens before me. The ventral 
edge of the right valve is abruptly incurved over the edge of the left 
valve, and its inner margin shows two or three fine concentric lines 
and numerous fine crenulations; while the inner edge of the dorsal 
margin shows similar crenulations, which are perhaps a little stronger 
than those on the ventral side. The ventral margin of the left valve is 
bent inwards almost rectangularly to the axis; the included surface, 
or that covered by the right valve, limited by a thin sharp slightly 
elevated ridge ; while on the anterior and posterior margins, the space 
between this ridge and the inner edge of the valve is contracted to a 
narrow well-defined groove. In older shells, the inner ventral edge of 
the right valve presents a strong groove for the reception of the ventral 
edge of the left valve. 
Surface essentially smooth, or so finely granulose as not to be visible 
