SPHJERIUM. 49 



of the shell ; striae very delicate ; epidermis greenish-yellow, somewhat 



darker in the region of the beaks ; valves slight, interior 



bluish ; hinge-margin somewhat rounded, narrow ; cardinal Fig. 46. 



teeth slight, assuming the shape of the letter V reversed ; 



lateral teeth elongated. 



Long. 0.56; Lat. 0.34; Diam. 0.21 inches. 

 Hab. North America, in the Big Prairie Creek and in s contractum 

 Greer s Creek in the State of Alabama. (Cabinets of the 

 Smithsonian Institution, Lewis, Sho waiter, Wheatley, and Prime.) 



Compared with S. transversum, to which this species is closely 

 allied, it is found to be smaller, less elongated, the beaks are 

 smaller, the anterior and posterior margins less disproportionate 

 and the hinge-margin is more rounded. 



Found by Dr. Showalter, in not inconsiderable number. 



24. Spliaerium securis, PKIME. Animal pinkish, syphons of the 

 same color. 



Shell rhombic-orbicular, ventricose, subequilateral, both sides of very 

 nearly the same length ; anterior margin a little curved ; posterior margin 

 abrupt, forming an obtuse angle with the hinge-margin: 

 basal margin much longer than the superior margin, round- Fig. 47. 

 ed ; beaks large, calyculate, slightly inclined towards the 

 anterior, very approximate at apex ; valves slight, very con 

 vex, especially in the region of the umbones ; striae delicate, 

 regular, hardly perceptible ; epidermis glossy in some cases, g securis. 

 very variable in color, but generally of a greenish-horn, 

 at times of a brilliant yellow or straw color ; hinge-margin curved, narrow ; 

 cardinal teeth very small, united at base ; lateral teeth slight, elongated, 

 very narrow. 



Long. 0.37 ; Lat. 0.31 ; Diam. 0.25 inches. 



Hab. North America, in the States of Massachusetts, Vermont, Rhode 

 Island, Pennsylvania, Michigan, New York, and in Canada. (Cabinets of 

 Jay, Lewis, Prime, and Smithsonian Institution.) 



Cyclas securis, PRIME, Bost. Proc. IV, 1851, 160. Ann. N. Y. Lyceum, 



V, 1851, 218, pi. vi. 



C. cardissa, PRIME, Bost. Proc. IV, 1851, 160. 

 C. crocea, LEWIS, loo. sub. cit. VI, 1854, 25. 



Found plentifully at Cambridge, Mass. I cannot see differences 

 sufficient between S, securis and C. cardissa to separate them ; 

 C. cardissa is more globose, transversely shorter, more elevated, 

 4 



