OPIS. 
165 
Pam. GAMMARIBM. 
Adapted for swimming ; mandibles with a palpus. Body 
generally compressed. Antennae ending in a flagellum, 
not like legs. Two posterior caudal appendages sometimes 
short. Legs long and slender. The antennae assist the 
Gammari very much in obtaining the minute particles of 
food which abound in the water. Say^ describes a species 
as striking an object of a proper size, 'when it comes within 
a moderate distance of its mouth, into the grasp of the 
four front feet, the first pair of which seem to be most 
employed. 
Gen. 62. OPIS, Kroger-. 
First pair of legs armed with claws of great size ; second 
pair of legs not subcheliform ; upper antennae with an ap- 
pendage, and thick at the base. 
A species of Opts, said to be 0. typica , has been found 
in Ireland (Strangford Lough, W. Thompson). This was 
picked off Algae brought up from a depth of fifteen to 
twenty-three fathoms, where they grew on soft sandy ground. 
* Journal of the Acad. Nat. Sc. Phil. i. p. 375. 
