100 



ually striated with numerous, equal, parallel, regular impressed 

 Hues, not visible to the unassisted eye, and obsolete on the poste- 

 rior margin ; basal edge within crenate ; color pale-livid, with two 

 longitudinal whitish rays before the middle, both within and with- 

 out. 



Var. a. Whitish. Var. I. Yellowish. Breadth from half an 

 inch to three-fifths. Inhabits the coasts of New Jeraey and Mary- 

 land. Cabinet of -the Academy and Philadelphia Museum. 



Very numerous under the surface of the sand, which is exposed 

 at the recess of the tide. A wave, by removing the surface of the 

 sand, exposes a great many individuals to view, at its refluence ; 

 these immediately penetrate the sand, and before the recurrence of 

 the surge they are concealed. 



They are preyed upon by several shore birds and fish ; the drum 

 (^Scisena chromii) and sheep's-head (Sjmrns ovicejfhalus) are 

 sometimes caught in the surf in considerable numbers, whilst in 

 pursuit of them. 



Amphidesma orbiculata. — Shell orbicular, somewhat com- 

 pressed ; beak nearly central, and a little prominent ; posterior 

 slope a little concave near the beak ; lunule small ; valves slightly 

 wrinkled transversely } ajiterior submargin with an obsolete very 

 obtuse undulation, and with a few longitudinal obsolete lines ; 

 color dirty white ; hinge with two lamellar teeth, the posterior one 

 placed near to the primary tooth, and shorter than the anterior 

 one ; interior ligament cavity profound, fusiform, parallel with the 

 anterior slope, originating at the extreme tip of the beak, and ter- 

 minating nearly opposite to the middle of the anterior lamellar 

 tooth. 



Length one inch and one-tenth. Breadth one inch and one- 

 tenth. Inhabits the coast of Georgia. Cabinet of the Academy 

 and Philadelphia Museum. 



Appears to be a rare species ; the largest I have seen is one inch 

 and two-fifths in bread tli. 



Amphidesma .^qualis. — Shell orbicular, slightly oblique, 

 polished, white, witli very minute and numerous concentric 

 wrinkles near the margin, which are obsolete on the disk and 

 umbo ; lateral teeth none ; primary teeth two in the left valve and 

 one in the other ; interior ligament cavity subfusiforni, as long as 

 the exterior ligament. 



