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6 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, flattish 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 strie 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 ; 
