158 AMERICAN MARINE CONCHOLOGY. 



Genus MEKCENARIA, Schumacher. 

 Essai Nov. Gen., 135. 1817. 



1. M. MERCENARIA, Linnaeus. Figs. 388, 389, 390. 



(Venus.) Syst. Nat., edit. xii. 1131. 1767. 

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



VARIETY. 



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



Shell solid, obliquely ovate, very inequilateral ; lunule 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 2J 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 the wampum or colored beads, constituting the specie cur- 

 rency of the Indians, was formerly manufactured. 



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



(Venus.) Journ. Philad. Acad., vii. 251. 1837. 

 Mercenaria fulgurans, Tryon, Am. Journ Conch., i. 1865. 

 ? Venus prwparca, Say, Journ. Philad. Acad., ii. 271. 1822. 



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

 prominent recurved concentric laminae, more elevated at the sides; 

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

 date, denned by a deep groove ; posterior extremity slightly emar- 

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

 grooved ; muscular impressions very large ; inner margin regularly 

 crenulated. 



Length 5 to 6 inches. 



North Carolina, southwards. 



Mercenaria fulgurans, Tryon, (Fig. 391) appears to be a younger 



