AND OTHER FAMILIES. 107 



lobe; anterior cicatrices confluent; posterior cicatrices confluent; dorsal 

 cicatrices placed under the cardinal teeth; cavity of the shell deep; 

 cavity of the beaks shallow ; nacre bluish white. 



Remarks. — This species most resembles the Mi.smoilonfa marginafa 

 (Say), but may be distinguished by its more cylindrical form, and its 

 want of undulations on the posterior slope. It differs also in the round- 

 ness of the umbonial slope, and in the rays. In the marginata the 

 rays are more interrupted and scattered, being sometimes quite spotted. 



Cyrena rotundata. Plate XVII. fig. 51. 



Testd rotundatd, sublenficulai-i, siibwqiillaterali, transversim rugaWl ; cUvo pos- 

 teriori rugoso ; valvulis crassis ; natibus pari'is, acutis, cont ignis ; dentibus car- 

 dinalibus subbijidis, laterulibus longis, minute serralis, reclisque ; murgarildulbd 

 et purpurea. 



Shell round, sublenticular, nearly equilateral, transversely wrinkled, rugose on the 

 posterior slope ; valves thick; beaks small, pointed, touching ; cardinal teeth disposed 

 to be bifid 5 lateral teeth long, straight and minutely serrulate; nacre white and pinkish. 



Hab 



My Cabinet. 

 Diam. 1-5, Length 29, Breadth 3-3 inches. 



Shell round, sublenticular, nearly equilateral, transversely and rather 

 minutely wrinkled, rugose on the posterior slope ; substance of the 

 shell thick ; beaks small, pointed, touching ; ligament very short and 

 thick; epidermis yellowish brown before and dark brown behind; 

 anterior slope furnished with a lanceolate mark formed by two curved 

 yellow lines, which pass from the beaks to the anterior margin ; pos- 

 terior slope rugose, furnished with obsolete oblicjue folds ; cardinal teeth 

 disposed to be bifid ; lateral teeth long, straight and vtv^ minutely ser- 

 rulate; cicatrices scarcely perceptible; cavity of the shell rather shallow; 

 cavity of the beaks subaugular ; nacre white and pinkish. 



Remarks. — This beautiful and fine large species was sent to me 



