56 CONTRIBUTIONS 



ing to be moved. Its rough interior and large deeply im- 

 pressed anterior cicatrix are remarkable. 



L. rotunda. Plate 1. Fig. 28. 



Description. Shell orbicular, compressed, equilateral, 

 concentrically and finely striate, tlattish over the umbones, 

 folded before ; substance of the shell thick ; lunule small, 

 lanceolate ; beaks very small, pointed, recurved ; cardinal 

 teeth indistinct; cicatrices impressed, the anterior one 

 rather long ; lines of growth numerous near the margin ; 

 cavity of the shell very shallow, having rather a large fur- 

 row across its centre ; margin entire. 



Diam. .6, Length 1.1, Breadth 1.1, of an inch. 



Observations. Single valves of two individuals only have 

 come into my possession. Its orbicular form and beautiful 

 concentric striae distinguish this species. In these two 

 specimens there are no marks of growth except near to 

 the margin, where on one specimen there are four, on the 

 other seven. These cause a thickening of the margin. 



L. cornuta. Plate 1. Fig. 29. 



Description. Shell orbicular, ventricose, inequilateral, 

 concentrically striate, angular before, folded and emargin- 

 ate behind ; substance of the shell thick ; lunule impress- 

 ed, being bounded by a ridge ; beaks elevated, pointed, 

 recurved ; anterior lateral tooth nearly round, equidistant 

 between the beak and angle ; posterior lateral tooth some- 

 what compressed, equidistant between the beak and fold ; 



