INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 469 



nassa obsoleta, (p. 354, Plate XXI, fig. 113,) which creeps over the flats 

 and muddy bottoms in countless multitudes, sometimes almost covering 

 the entire, surface. When left by the tide, on the flats, especially in cold 

 weather, they will creep into the small pools and depressions of the sur- 

 face, where they often huddle together in great crowds, sometimes form- 

 ing many layers, one above another. This is probably the most abundant 

 shell, of any considerable size, on the coast of the United' States. It 

 occurs abundantly from the Gulf of Mexico to Massachusetts Bay. It is 

 essentially a scavenger, and owing to its vast numbers its services in 

 that line must be of great value. It occurs far up the estuaries, where 

 the water is decidedly brackish, but nourishes equally well on the outer 

 shores. 



The Littorinella minuta (Plate XXIV, fig. 140) also occurs in vast 

 numbers on the mud-flats, and in the pools and ditches of the salt- 

 marshes, but it is a small and inconspicuous species. It is, however, not 

 overlooked by the small fishes and various aquatic birds, for they feed 

 largely upon it. 



The Melampus bidentatus (Plate XXV, figs. 109, 169a) is also extremely 

 abundant on the muddy salt-marshes, creeping over the general surface, 

 or in the shallow pools and ditches, and among the grass, creeping up 

 the stalks. In shallow water, where not too brackish, the Bulla solltaria 

 (Plate XXY, fig. 161) is sometimes found in considerable numbers, 

 creeping over soft, muddy bottoms. It is a favorite article of food with 

 the flounders. 



Among the Lamellibranchs, one of the most common species is the 

 Modiola plicatula, (Plate XXXI, fig. 258,) which occurs everywhere on 

 the muddy banks at and above high- water mark, and also over the salt- 

 marshes, along the borders of ditches and streams, and wherever there 

 is sufficient moisture, partially imbedding its shell in the mud or among 

 the roots of grass, and anchoring itself by means of a stout byssus. 

 The long clam, Mya arenaria, (p. 463) and the Macoma fusca, (Plate 

 XXX, fig. 222) are almost everywhere abundant on the shores between 

 tides. 



The " round clam," Venus mercenaria, (p. 359, Plate XXVI, fig. 184,) 

 occurs on the muddy bottoms in shallow water, often in great abundance, 

 especially where the mud is somewhat firm, or where there is an admix- 

 ture of sand, and the water is not very much freshened. This clam is usually 

 taken in such places by means of long-handled tongs, and sometimes 

 with the dredge. It is especially abundant in the estuaries and harbors 

 opening into Long Island Sound. The quantity of this clam taken 

 annually for food is enormous, but it is impossible, at present, to get re- 

 liable statistics, either for this or the long clam, for they are mostly taken 

 and sold, a few bushels at a time, by individual fishermen, and the 

 traffic is diffused along the whole coast, from Florida to Boston ; but 

 it is probable that more than 1,500,000 bushels are annually consumed. 



