AND OTHER FAMILIES. 219 



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 Masmodonta marginata 

 (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 rotund ATA. Plate XVII. fisr. 51 



o* 



Testd rotundatd, sublenficulari, subxquilaterali, iransversim rugatd ; clivo pos- 

 teriori rugoso ; vaivulis crassis ; natibus parvis, aculis, contiguis ; dentibus car- 

 dinalibiis subbijidis, lateralibus longis, minute serratis, reclisque ; margaritd albd 

 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 ; lateral teeth long, straight and minutely serrulate ; nacre white and pinkish. 



Hab 



My Cabinet. 

 Diam. 1-5, Length 2-9, 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 oblique folds; cardinal teeth 

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

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

 cavity of the beaks subangular; nacre white and pinkish. 



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



