[315] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 21 
species, found in the same situations, is the Mara levis Smirm; this is 
whitish in color, with black eyes. 
Two species of the genus Amphithoé also live under rocks at low water, 
but these, like the other species of this genus, construct tubes in which 
they dwell. The Amphithoé maculata (Plate IV, fig. 16) is much the larger, 
and constructs large, coarse tubes of gravel, bits of sea-weed, &c., and 
attaches them in clusters to the under sides of stones. They often leave 
their tubes, however, and may be found free among the weed or under 
stones. The color is generally dark green, though sometimes reddish, 
and there is often a series of light spots along the back, and the whole sur- 
face is covered with minute blackish specks; the eyes are red. The 
second species, Amphithoé valida SMITH, is much smaller, being gener- 
ally less than half an inch long. It is usually bright green in color, and 
has black eyes. It often lives among the bright green fronds of Ulva 
latissima, and its color is nearly that of the Ulva. 
Another amphipod, resembling a small Gammarus, about half an inch 
long, and light olive-brown or yellowish brown in color, is sometimes 
found in large numbers swimming actively about in the larger tidal 
pools, and occasionally darting into the growing sea-weeds for rest or 
concealment. This is the Calliopius leviusculus. It also often occurs 
in vast numbers swimming at the surface, far from land, not only in the 
sounds and bays, but out at sea, as for instance in the vicinity of St. 
George’s Bank and in the Gulf of St. Lawrence, where it is equally — 
abundant. It is devoured in large quantities by numerous fishes. 
The Hyale littoralis occurs near high-water, among algie, and in pools. 
The. Isopods are also well represented on the rocky shores. One 
of the most common is the Sphwroma quadridentata, (Plate V, fig. 
21,) which bears some resemblance, both in form and habits, to the 
** pill-bugs,’ which live upon the land. This species is found in abun- 
dance under stones and rocks, or creeping slowly about among the branches 
and roots ef sea-weeds, on their sides and upper surfaces, from low- 
water mark nearly up to high-water mark. In color it is exceedingly 
variable, for no two can be found that are alike ; but the colors, consisting 
of irregular blotches and dashes of dark gray, light gray, slate, greenish, 
and white, are so blended as to imitate very closely the colors of the bar- 
nacles and gray surfaces of the rocks where they live, and no doubt 
they derive considerable protection from their enemies by these imita- 
tive colors. When disturbed they curl themselves up in a ball and fall 
to the bottom. 
Another smaller and much more active species, which has a more 
slender form, is found in vast numbers creeping actively about over the 
rocks and barnacles, and especially beneath rocks and drift-wood. This 
is the Jara copiosa. It is also excessively variable in color, but shades 
of green, gray, and brown predominate, and cause it to imitate very ef- 
fectively the surfaces of the rocks covered with small green algie, where 
