158 AMERICAN MARINE CONCHOLOGY. 



Genus MERCENAEIA, Schumacher. 

 Essai Nov. Geu., 135. 1817. 



1. M. MERCENARTA, Liiinffius. Figs. 388, 389, 390. 



(Ve)ius.) Syst. Nat., edit. xii. 1131. 1767. 

 Mercenaria violacea, Schumacher, Essai, Nov. 135, t. 10, f. 3. 1817. 



VARIETY. 



Venns notata, Say, Journ. Philad. Acad., ii. 271. 1822. 



Sliell solid, obliquel}' ovate, very inequilateral ; Imiule heart- 

 shaped ; surface bluish-white, with numerous concentric, laminated 

 ridges, becoming obsolete on the middle; inner margin stained 

 with violet. 



The variety (perfect young or half-grown shells) has the surface 

 covered with fawn-colored zigzag markings, and the interior is 

 wholly white (Fig. 390). 



Usual length 3 inches, height 2^ inches. It sometimes attains 



much greater proportions. 



Massachusetts to North Carolina. 



This species is the common Round Clam, so much prized as an 

 article of food. Its aboriginal name of Quahog has now fallen 

 into disuse. It abounds in all our bays, a few inches below the 

 surface, from low-water mark to six fathoms. If taken from its 

 bed and placed on its side, it can, in the course of a single tide, 

 bury itself six inches. From the colored internal margin of the 

 shell tlie wampum or colored beads, constituting the specie cur- 

 rency of the Indians, was formerly manufactured. 



2. M. MORTONi, Conrad. Figs. 391, 392. 



iVenus.) Journ. Philad. Acad., vii. 251. 1837. 

 Mercenaria fulgura7is, Tryou, Am. Journ Conch., i. 1865. 

 f Ve7uis prceparca, Say, Journ. Philad. Acad., ii. 271. 1822. 



Shell very large, cordate, inflated, thick and ponderous, with 

 prominent recurved concentriclarainae, more elevated at the sides; 

 ligament margin arcuate. Umbones prominent; lunule large, cor- 

 date, defined by a deep groove ; posterior extremity sligiitl}- emar- 

 ginate ; cavity of the cartilage profound. Teeth large, prominent, 

 grooved ; muscular impressions very large ; inner margin regularly 

 crenulated. 



Length 5 to G inches. 



North Carolina., southwards. 



3Iercena7'iafulgurans, Tryon, ( Fig. 391) appears to be a younger 



