[367] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 73 
a certain extent, conditions similar to those of rocky shores, and conse- 
quently it is natural that certain rocky-shore species should be found in 
such situations. Only the more common and most important of these 
have been introduced into the list, however, for to include all the species 
to be found among oysters would uselessly extend the catalogue. 
Among the Crustacea we find a considerable number of species which 
have their proper homes on the muddy shores. Of the true crabs there 
are at least eleven species that constantly occur in these situations, but 
several of them, viz, Cancer irroratus, (p. 312,) Panopeus depressus, (p. 
312,) P. Sayi, (p. 312,) and Carcinus granulatus, (p. 312,) are found in 
greater numbers elsewhere, and depend largely upon the oyster-beds for 
their safety on these shores. The Carcinus granulatus, however, often 
resorts to the holes and cavernous places under the peaty banks of the 
shores, or along the small ditches and streams cutting through the peaty 
marshes near the shore. The marsh “fiddler-crab,” Gelasimus pugnax, 
is usually very abundant in the peaty banks and along the ditches and 
streams at and just above high-water mark, where it excavates great 
numbers of deep holes, often completely riddlin gthe soil. This species 
is, however, more at home along the borders of the estuaries and 
lagoons aud will be described more fully in that connection, as well as 
the Sesarma reticulata, which often occurs with it in both situations. 
The “ oyster-crab,” Pinnotheres ostreum, (Plate I, fig. 2, male,) is found 
wherever oysters occur. The female lives, at least when mature, within 
the shell of the oyster, in the gill cavity, and is well known to most con- 
sumers of oysters. The males (fig. 2) are seldom seen, and rarely, if ever, 
occur in the oyster. We found them, on several occasions, swimming 
actively at the surface of the water in the middle of Vineyard Sound. 
They are quite unlike the females in appearance, being smaller, with a 
firmer shell, and they differ widely in color, for the carapax is dark brown 
above, with a central dorsal stripe and two conspicuous spots of whitish, 
as indicated in the figure; the lower side and legs are whitish. The 
female has the carapax thin and translucent, whitish, tinged with pink. 
The Pinnixa cylindrica (Plate I, fig. 1) is a related species whicb is 
occasionally met with on muddy shores. It lives in the tubes of certain 
large Annelids in company with the rightful owner. The specimens 
hitherto met with in this region were either found free, or dug out of 
the mud, and it is uncertain with what worm they associate, though it 
is most likely to be the Nereis virens, but on the coast of South Carolina 
it lives, according to Dr. Stimpson, in the tubes of Arenicola cristata 
Stimpson. It has been found in the stomach of the ocellated flounder. 
The common edible-crab or “ blue-crab,” Callinectes hastatus, is a com- 
mon inhabitant of muddy shores, especially in sheltered coves and bays. 
It is a very active species and can swim rapidly; it is therefore often 
seen Swimming at or near the surface. The full-grown individuals gen- 
erally keep away from the shores, in shallow water, frequenting muddy 
bottoms, especially among the eel-grass, and are also found in large 
