20 GENERA OF SHELLS. 



long oval, slightly gaping at sides ; a cardinal 

 tooth in each valve, sometimes only in one. 



The psamrnoteae are merely degenerated psammobiae, 

 differing merely in having only one cardinal tooth on 

 the left valve ; or sometimes one valve has no teeth, and 

 the other two. They have not the form of the solen, 

 and their beaks are prominent, and they are destitute of 

 the irregular fold of the tellina. 



P. violacea, zonalis, solenoides, pellucida, serotina, Can- 

 dida, tarentina, donacina, variegata. 



NYMPHACEA TELLINARIA. 

 I. HAVING ONE OR MORE LATERAL TEETH. 



TELLINA. Shell transverse or orbicular, gen- 

 erally flattened ; anterior side angular, margin 

 inflexed, or presenting at the edge a flexuous 

 and irregular fold ; one or two cardinal teeth 

 on the same valve ; two lateral teeth, often re- 

 mote. 



The tellinae are readily known by the flexuous fold 

 near the short side on their superior margin ; almost 

 all of them have also lateral teeth, which are flattened 

 on one valve. They are marine shore shells, slightly 

 or not at all gaping at the sides, often smooth, some- 

 times scaly, and in general adorned with lively colors. 

 In the tellina, as well as the donax and capsa, the 

 ligament is on the shorter side, and is wholly external. 

 The valves of the same shell, though equal in contour, 

 are not perfectly similar ; sometimes one is more pro- 

 tuberant than the other, and sometimes the striae of 

 one valve, or of one of its sides, are not like those on 

 the other. 



(a. oblong.) T. radiata, unimaculata, semizonalis, macu- 



