GREY CHALK MARL. 127 



Valves longitudinally costated ; costae radiating, decussated by con- 

 centric, transverse striae, and sulci ; posterior side truncated, cordiform ; 

 anterior side produced ; beaks incurved. 



This species, in its general form, approaches Cardium hibernicum 

 (Min. Conch, tab. 82, figs. 1, 2.) but is distinguished by its numerous 

 transverse sulci, the absence of the central protrusion, and by the posterior 

 side being crossed by diverging striae. 



The length of this cast rather exceeds its width. The margin of the 

 posterior side is raised, and a gentle depression is in consequence formed 

 round the centre, which is somewhat elevated. The termination of the 

 anterior side is unknown; the dotted outline in the figure indicates its 

 probable form. The beaks are smaU and incurved. 



The longitudinal ribs pass in a radiating manner, from the beaks to 

 the margin ; but are not visible on the posterior side. The sulci by which 

 they are decussated, arise from the depression beneath the beaks, from 

 whence they diverge across the posterior area, and becoming concentric, 

 terminate on the edge of the anterior slope. The margin of the valves is 

 entire. 



Tab. XXV. fig. 3. A cast from near Brighton. The shell itself is un- 

 known. 



Localities. Brighton, Hamsey, Middleham, OfFham. 



51. Pecten Beaver L Tab. xxv. fig H. 



Depressed, suborbicular, with diverging longitudina costae; ears 

 nearly equal to the width of the shell ; margin irregularly undu- 

 lated. 



The costae are about twenty in number, and diverge from the centre 

 of the hinge to the margin. The ears are almost equal to the transverse 

 diameter of the shell. 



This species is from 2*5 inches to 3 inches in length, and is commonly 

 in a good state of preservation. 



In almost every example the internal surface only^is exposed, the shell 

 being attached to the marl by the outer side ; in a small portion which I 



