176 U. S. BUREAU OF FISHERIES 



NATURAL HISTORY OF THE SCALLOP 



SHELL, 



The peculiar shell outline, nearly circular except for the built-out 

 or " eared '' hinge section (see photographs of scallop shell, figs. 1 

 and 2), generally is sufficient to characterize a bivalve as a scallop. 

 The ribs or rays, spreading fanlike from the umbos, or beaks, and 

 not so much thickenings as corrugations, help to give strength with 

 lightness to the thin but hard shell. The upper or left valve or half 

 shell is cupped less deeply and is much darker than the lower or 

 I'ight valve, sometimes termed the " breast " by scallop fishermen. 

 "The valves are secured, one to the otlier, at the long, straight hinge 



Fig. 1. — Exterior viow of loft and right valves of a scallop shell. The lower or 

 right valve, shown at the right, contains the byssal notch 



by a flexible strip, the ligament, and, in part, by the thick, pyramidal 

 cartilage, the principal function of which is. springlike, to open the 

 shell when it is not held closed bv the adductor muscle. 



SOFT PARTS 



The general shape and arrangement of a number of the soft parts 

 are shown in the accompanying photograph. (Fig. -3.) In general, it 

 may be noted that the spread-out arrangement, the lack of fusion 

 into a relatively homogeneous mass, is unusual in food molliisks. 

 The mantle, one lobe of which lines each valve, is notable for its 

 muscular border with numerous tentacles and eyes. 



' For more dotailed accounts the reader is referred to A Report upon the Scallop Fish- 

 ery of Massachusetts, by D. L. Belding, Boston. 1910 ; Shellfish Industries, by .1. L. 

 Kellogg, Henry Holt & Co., New York, 1910; and A Contribution to Our Knowledge of 

 the Morphology of Lamellibranch Molluslss, by J. L. Kellogg. Bull., U. S. Fish Commission, 

 vol. 10, 189;i. " The Habits, Anatomy, and Embryology of the Giant Sea Scallop iPrcte^i 

 tenuicontatus Mighels), by O. A. Drew (University of Maine Studies Xo. 0. 19(i6l, is 

 excellent for tliis allied form. 



