PLEIOCENE FOSSILS. 55 



In this well-defined species, the whole shell, which is rather thin, is covered with 

 elevated lines of growth, the spaces between which are covered with fine concentric stria?. 

 The beaks approximate, and the inner surface of both valves is covered with radiating 

 lines. 



It occurs sparingly in the Meiocene of Virginia, and is found living along the eastern 

 coast, as far north as Rhode Island. 



Plate XVIII. Fig. 1, Interior of right and exterior of left valve. 



Locality. Darlington District. 



LHCIXA AXODONTA.— Say. 



Pi.atk XV11I. Fig. 2. 



Lucina anodonta, Say, Jour. Ac. Nat. Sci., Vol, 4, p. 146, pi. 10, fig. 9. 

 Lucina anodonta, Say, Foss. Ter. For., p. 39, pi. 20, fig. 4. 



L. testa crassa, compressa, sub-rotundata, concentrice rugosa; latere anali rotundo; latere 

 buccali fluxuoso, sub-angulato; lunula excavata. 



Description. Shell thick, compressed, nearly orbicular, with concentric wrinkled 

 stride; anal side round; buccal margin somewhat angular; lunule excavated. 



This shell, though readily distinguished from the other species of the genus, is some- 

 what variable. In the young state it is thinner and more compressed. 



Towards the buccal side, an irregular radiating ridge extends from the umbones to the 

 pallial margin, and a similar, but shorter one, is often found on each side of the lunule. 

 Two obsolete folds occur on the anal side of the valves. On the inside there is a callus, 

 resembling a rough muscular impression, which extends from the elevated interior edge of 

 the hinge-plate to the buccal muscular impression, giving the cavity, at the beaks, an 

 angular appearance. 

 15 



