[53] FISHERIES OF THE UNITED STATES. 237 



Modiola modiolus, Turton. 



This, the great "horse-mussel," is found from Greenland southward to 

 New Jersey on the Atlantic, and from the Arctic south to Monterey on 

 the Pacific coast. It is more abundant north of Cape Cod than to the 

 southward, and is found from low- water mark to 80 fathoms. It is fossil 

 in (he Post-Pliocene formations of Massachusetts and Canada. The 

 horse-mussel is usually located in crevices between rocks, or bedded in 

 the gravel; and along the coasts is almost entirely confined to rocky bot- 

 toms. Its large size and brown, hairy epidermis, sufficiently distin- 

 guish it from other species. Though occasionally used for bait, and 

 available for food, it is at present of no commercial importance. 



Peeten irradians, Lamarck. 



This is the common "scallop" of the eastern coast. It extends from 

 Texas and the Gulf of Mexico to Cape Cod, and is occasionally found 

 north of that point. It is fossil in the Post-Pliocene of North Carolina 

 and Florida, in the Pliocene of South Carolina, and in the Miocene of 

 Maryland. 



The "scallop" is found on sandy and shelly bottoms, in sheltered lo- 

 calites, but usually prefers those points where the eel-grass abounds and 

 where there is more or less mud on the bottom. During the summer the 

 young shells may be seen clinging to the eel-grass or sea-weed in large 

 numbers, and in the autumn the mature animals are found in the shallow 

 waters along the shores in great abundance. Also after storms great 

 quantities are thrown upon the beaches. But the scallop is nomadic; 

 no one locality can be sure of its crop, no matter how abundant the 

 animals may have been during the previous seasons. Indeed, some of 

 the harbors of Long Island are visited by scallops in numbers but once 

 in four and five years, and at other points the appearance and disappear- 

 ance is irregular. Unlike many other bivalve mollusks, the Peeten irra- 

 dians is not fixed immovably to some foreign object; is not anchored by 

 a network of threads or "byssus," nor is it compelled to creep slowly 

 along the surface of the mud or sand by means of a "foot" however 

 muscular and strong. On the contrary, it is a very active swimmer, and by 

 opening and energetically closing its valves, it forces the water from the 

 gill-cavity, the reaction driving the animal backward through the water. 

 It is very watchful, quickly perceiving an enemy, and when alarmed, 

 deserts the matted leaves of eel-grass, its usual habitation, and takes 

 to the bottom. In moving from place to place, the animals make a suc- 

 cession of leaps to the surface, each time advancing some yards on their 

 journey, and great schools of those curious shells are sometimes seen 

 thus darting about in the water. The spawning takes place during the 

 summer, and continues as late as September. The size of the shells at 

 that time is shown in the series illustrating the rate of growth. The 

 growth during the autumn mouths is quite rapid, but it is claimed that 



