[479] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 185 
Many small fishes frequent the patches of eel-grass, and find there 
abundance of food and unusual safety from their enemies. 
Among the most comm®n Crustacea found among the eel-grass are 
the edible crab, Callinectes hastatus, (p. 367;) Panopeus Sayi, (p. 313) 
P. depressus, (Plate I, fig. 3;) Hupagurus longicarpus, (p. 313 ;) the prawn, 
Palemonetes vulgaris, (p. 369, Plate IT, fig. 9;) the common shrimp, Cran- 
gon vulgaris, (p.339, Plate IL, fig. 10;) the green shrimp, Virbius zosteri- 
cola, (p. 369, Plate III, fig. 11;) Mysis stenolepis, (p. 370, Plate III, fig. 125) 
M. Americana, (p. 370;) Idotea irrorata, (p. 316, Plate V, fig. 23;) Melita 
nitida, (p. 314.) The common prawn (Plate II, fig. 9) has its true home 
among the eel-grass, and here it occurs in countless numbers. Its trans- 
lucent body, marked with irregular, ill-defined, dark blotches and spots, 
admirably adapts it for concealment among the discolored and dead 
leaves of the plant, at or near the bottom. 
Where the eel-grass grows on sandy bottoms the common shrimp is 
searcely less abundant. The Virbius is often abundant, associated with 
the common prawn, and having similar habits. Al these shrimps and 
prawns are eagerly devoured by the fishes. The Idotea irrorata is gen- 
erally very abundant, and clings firmly to the leaves of the eel-grass 
lengthwise. Its body is generally curiously and variously colored with 
green and brown, &c., and these colors are often so arranged as to imi- 
tate very perfectly the colors of the eel-grass when partially dead or 
discolored. Sometimes the right or left half of the body will be bright 
green, while the opposite half will be dark brown. In other cases there 
will be a dorsal bright green stripe, while the sides will be dark brown, 
just like one of the leaves of the eel-grass that is discolored at the 
edges, but green in the middle. More commonly these colors are ir- 
regularly disposed in blotches. 
The Erichsonia attenuata HARGER, is a remarkably slender species, 
which also lives clinging to the eel-grass. Its colors are green and 
brown, and quite variable. 
Several species of Amphipods are also abundant among the eel-grass. 
One of the most common of these is the Gammarus mucronatus, (p. 466,) 
which is easily distinguished by the dorsal teeth on the abdominal seg- 
ments. Microdeutopus minax SMITH, is a very small species, which 
sometimes occurs in great abundance in the small brackish ponds. It 
is remarkable for its relatively large and very broad hands, armed 
beneath with three prominent teeth. The hands are nearly as large as 
the entire body. 
Among the Mollusks several interesting species occur. The Ilyanassa 
obsoleta, (p. 371, Plate XX, fig. 113;) Bittium nigrum, (p.305, Plate XXIV, 
fig. 154;) and Astyris lunata, (p. 306, Plate X XI, fig. 110,) are generally 
the most abundant species. The Nassa vibex (p. 371, Plate X XI, fig. 114) 
is met with occasionally, living on and about the roots of eel-grass, but 
itis an uncommon shell in our waters, though quite abundant on the 
southern coasts. The Crepidula convexa (p. 371, Plate XXIII, fig. 128) 
