158 AMERICAN MARINE CONCHOLOGY. 
Genus MERCENARIA, Schumacher. 
Essai Noy. Gen., 185. 1817. 
1. M. mercenaria, Linneus. Figs. 388, 389, 390. 
( Venus.) ~Syst. Nat., edit. xii. 1131. 1767. 
Mercenaria violacea, Schumacher, Essai, Nov. 1385, t. 10, f. 38. 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 24 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. 1887. 
Mercenaria fulgurans, Tryon, Am. Journ Conch., i. 1865. 
? Venus preparca, Say, Journ. Philad. Acad., ii. 271. 1822. 
Shell very large, cordate, inflated, thick and ponderous, with 
prominent recurved concentric laminze, more elevated at the sides; 
ligament margin arcuate. Umbones prominent; lunule large, cor- 
date, defined 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 
