MARINE MOLLUSCA OF THE UNITED STATES. 193 
England coast and Gulf of St. Lawrence, but has probably been 
transplanted to these localities. The lower valve is sometimes 
ornamented with red or violet rays. 
2. O. BOREALIS, Lamarck. Figs. 530, 531. 
Anim. sans Vert., vil. 220. 1822. 
Shell rounded-ovate, the upper valve covered with membranous 
scales, the lower valve irregularly spiny-ribbed and foliaceous. 
Length 3 to 6 inches, breadth about 2 to 5 inches. 
New England, New York. 
This species is apparently very distinct from the preceding ; it 
is smaller, wider, has not the lengthened beak of the lower valve 
of Virginiana and the surface is much rougher. It is very closely 
allied to O. edulis of Europe. 
3. O. TRIANGULARIS, Holmes. 
Proc. Elliott Soc. Nat. Hist., 29. 1856. 
Shell subtriangular, subequivalve, subequilateral, thick, lami- 
nated; beaks produced, acutely pointed, angular, and slightly 
curved towards each other; margins rounded ; cavity of the shell 
circular; muscular impression very large in proportion to the size 
of the shell, and placed near the margin of the base. 
South Carolina. 
Dr. Holmes states that this shell resembles O. edulis of Europe 
but is more regular in form. Its large muscular impression, 
pointed beaks, and triangular shape distinguish it from that 
species. I am not acquainted with this shell. 
4. O. EQUESTRIS, Say. Figs. 532, 533. 
Am. Conch., vi. t. 58. 1884. 
Shell small, ovate-triangular, more or less folded longitudinally ; 
lateral margins near the hinge with from six to twelve denticu- 
lations of the superior valve received into corresponding cavities 
of the inferior valve; superior valve depressed, but slightly folded ; 
inferior valve convex, attached by a portion of its surface, the 
margins elevated, folds unequal, much more profound than those 
of the superior valve; hinge very narrow, and curved laterally 
and abruptly. 
North Carolina to West Indies. 
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