LOWER HELDERBERG ROCKS. 97 S 



Leperditia Imdsonica ( n. s.)- 



Plate LXXIX A. Fig. 7 a, b, c. 



Carapace valves nearly equal, slightly oblong, the length being to the 

 width as three to two : hinge-line less than the greatest width, broadest 

 at the posterior third ; dorsal line straight ; ventral and anterior ex- 

 tremities obliquely rounded, the posterior extremity broadly rounded, 

 the anterior cardinal angle a little produced, and a narrow border 

 extending a little below the dorsal line on each valve. The greatest 

 convexity of the surface is central, or a little anterior to the centre, and 

 not quite corresponding on the two valves. The antero-dorsal tubercle 

 is but slightly developed, distant from the anterior extremity, and 

 nearer the central tubercle : central tubercle not raised above the 

 general convexity of the surface, and distinguishable only by the re- 

 flection of light. Ventral edge of the right valve curving over the edge 

 of the left valve, which is abruptly bent inwards beneath the opposite 

 valve, the limit of the included surface being marked by a sharp ele- 

 vated line : substance of the valves thick. 



Surface smooth, or without visible markings under an ordinary lens. 



This species differs from L. alta in its greater proportional width and gibbosity : 

 the anterior tubercle is proportionally more distant from the extremity; the ventral 

 margin of the right valve is less abruptly bent inwards, and leaves no angle on the 

 line of incurvation, which is less extended in this species, while the shell is thicker 

 and the ventral margin more oblique. 



Fig. 7 a. View of specimen, natural size. 



Fig. 7 b. The same enlarged two diameters. 



Fig. 7 Cm Profile view, showing the nearly equal convexity of the two valves, and length 

 of the hinge-line. 



Geological position and locality. Xear the base of the Lower Helderberg group : 

 Becraft's mountain, near Hudson. 



