^"khu!"!!'] I'K'OCKEDING.S OV THE NATIONAL MUSEUM. 323 



otherwise than the color charactin' above iiieiitione(l,an<l that is of little 

 importance. lieev^e says of his forrida, which it will be observed is 

 one of the all white forms, that it is "concentrically sculptured with 

 tine cord-like stria', alter the nuinner of A. ()rbi(j)(yiy The roundness 

 or sharpness of the strite varies more or less in all. The depression 

 of the lunule also varies somewhat, but is usually rather deeply sunken. 

 In all, the closeness, delinition, or sharpness of the conceutrit; strife^ 

 is greater toward the anterior and posterior edges of the valve than 

 in the central portion or area. The hinge characters are the same in 

 all, and the interior of the valves are alike in the shape or outline, 

 angle and depth of the siiuis, and muscular scars. The valves in all 

 of these, whether young or old, large or small examples, are heavy, 

 solid, and thick, with thick hinge margins and long and rit>ther deeply 

 scar])ed liganiental area. 



The foregoing critical comparison, it will be noticed, practically 

 unites the live so called species, the only differences being those of 

 coloi', and the greater or less roundness, evenness, or shaipness of the 

 concentric lira^ Now, variation in these cliaracttu's, it is well known, 

 is a local matter dei)endent u[)on or affected by local causes or condi- 

 tions, such as the character of the sea bed at the spot from which the 

 specimens were obtained. Where the sea bed is nearly clear sand with- 

 out mud, gravel, etc., the shells are whiter, more evenly and regularly 

 sculi)tured, witli a more porcellaneous surface- than from localities where 

 graxel, nuid, and (;lay prevail. The presence of mud, particularly 

 clayey mud, has nuicli to do with the coloration or staining of the shell. 



Any i)erson who has collected the hard-shell clam VcmiH mcrccnaria 

 of the Atlantic seaboard, at many or diiferent places throughout the 

 range of said species, or the Mactra or Mya of the same faunal region, 

 must have noti(;ed tlie relation of color to the character of the sea bed. 

 ('onvexity is another somewhat variable factor, some examples being 

 more tumid than others. 



Keeve's radiata is no doubt a distinct form, thougli iaocardia is doubt- 

 fully distinct, and may hereafter, with abundant material for compari- 

 son, be regarded lis a synonym. 



30. Dosinia Orbignyi Duuker. 



;= 1). (ifriatna (iray. 

 ^^ 7'. Iicjxitiid riiilij)])!. 



Many odd valves. Porto Grande (^lus, No. Ili5385), Sei)arable 

 horn Jibula, etc., only by tlie color stain — no doubt the same species. 



31. Dosinia isocardia ])mik(i. 



One left valve, beach. Porto (Jrande (Mus. No. lL'5;j-S8). 



Suborder TELLINACEA. 



Family DONACID^E. 



Genns DONAX Limu'. 

 32. Douax rugosus Liun6. 



