20 AMERICAN CORBICULAD^E. 



Fig. 15. anterior tooth in the right valve rudimentary, 



central slightly bifid ; lateral teeth compressed, 

 the cavity of the anterior tooth in the right valve 

 united to the cardinal by a well-defined fissure ; 

 anterior tooth approximate ; sinus short, curved 

 at end. 



Long. 0.86 ; Lat. 0.90 ; Diam. 0.53 inches. 

 21 ; &quot; 22 ; &quot; 13 mill. 



C. ordinaria. Bab. South America ? (Cabinet of Prime. ) 



Compared with C. regalis, it is larger, transversely shorter, 

 less heavy, less produced on the posterior side, fuller, the beaks 

 are more prominent, the striae are less regular and more delicate, 

 the epidermis is not so greenish in color. Smaller and less full 

 than (7. radiata and C. solida. A rare species. 



14. Cyrena iiitidula, DESHAYES. Shell transversely oval, fra 

 gile, inequilateral ; anterior side shorter, rounded at end ; posterior side 

 rounded or subtruncated ; striae light ; epidermis greenish ; beaks tumid, 

 acute, opposite ; valves light, somewhat compressed ; interior pale violet ; 

 sinus short, triangular, acute ; hinge-margin very narrow ; cardinal teeth 

 unequal, divergent, narrow, bifid ; lateral teeth subequal, small. 



Long. 1.12; Lat. 1.00; Diam. 0.68 inches. 



&quot; 28 ; &quot; 25 ; &quot; 17 mill. 

 Hab. South America ? (Cabinet of Cuming.) 



Cyrena nitidula, DESHAYES, Proc. Zool. XXII, 1854, 23. 



The specimen in the collection of Mr. Cuming, from which this 

 description was prepared, has no locality assigned to it ; the fact 

 of its having a sinus places it without a doubt among the species 

 from America, and I am strongly inclined to think that it is a 

 native of South America. 



15. Cyrena placens, HANLEY. C. testa suborbiculari, subventri- 

 cosa, insequilaterali, nitida, concentrice, sulcato-striata,&quot; epidermide irrido- 

 flavescente induta ; margine ventrali convexo ; dorsali, utrinque declivi et 

 convexiusculo ; natibus erosis ; ligamento fulvo, depresso, angusto ; lumula 

 nulla ; superficie interna purpurea ; dentibus lateralibus minutissime 

 rugulosis haud autem crenatis, antico brevi et subapproximato. 



Long. 1.75 ; Lat. 1.50 inches. 



Hab. South AmericI ? (Cabinets of Hanley and the Jardin des Plantes.) 

 Cyrena placens, HANLEY, Proc. Zool. XII, 1844, 160. Index test. 

 suppl. pi. xiv, f. 52. 



