(469] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 175 
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. Itis 
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 flourishes 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 XXYV, figs. 169, 169) is also extremely 
abundant on the muddy salt-marshes, créeping over the general surface, 
orin the shallow pools and ditches, and among the grass, creeping up 
the stalks. In shallow water, where not too brackish, the Bulla solitaria 
(Plate XXV, 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 XXAI, 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 waterisnot very much freshened. Thisclamisusually 
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. 
