INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 479 



Many small fisbes frequent the patclies of eel -grass, and find there 

 abundance of food and unusual safety from their enemies. 



Among the most common Crustacea found among the eel-grass are 

 the edible crab, CaUinectes hastatm, (p. 3(!7 ;) Panopeus i^ayi, (p. 312;) 

 P. depressus, (Plate I, fig. 3 ;) Eupagnrus longicarpus, (p. 313 ;) tlie prawn, 

 Palannonctes vulgaris, (p. 3G9, Plate II, fig. ;) the common shrimp, Cran- 

 gon vulgaris, (p. 339, Plate III, tig. 10;) the green shrimp, Virhius zosferi- 

 cola, (p. 309, Plate III, tig. 11;) Mysis stenolepis, (p. 370, Plate III, tig. 12;) 

 M. Americana, (p. 370;) Idotea irrorata, (p. 310, Plate V, fig. 23;) Melita 

 nitida, (p. 314.) The common prawn (Plate II, tig. 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 jilaut, at or near the bottom. 



Where the eel-grass grows on sandy bottoms the common shrimp is 

 scarcely less abundant. The Virhius is often abundant, associated with 

 the common prawn, and having similar habits. All these shrimps and 

 prawns are eagerlj^ 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 Mill 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 Ericlisonia 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. 400,) 

 which is easily distinguished by the dorsal teeth on the abdominal seg- 

 ments. Microdetifopus 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 

 th.e entire body. 



Among the Mollusks several interesting species occur. The Ilyanassa 

 obsoleta, (p. 371, Plate XXI, fig. 113;) Bittium nigrmn, (p. 305, Plate XXIV, 

 fig. 154;) and Astyris lunata, (p. 300, Plate XXI, fig. 110,) are generally 

 the most abundant species. The Kassa vibex (p. 371, Plate XXI, fig. 114) 

 is met with occasionally, living on and about the roots of eel-grass, but 

 it is an uncommon shell in our waters, though quite abundant on the 

 southern coasts. The Crepidula convexa (p. 371, Plate XXIII, fig. 128) 



