ORDER AMPHIPODA — ORCHESTIA. 35 



ORDER III. AMPHIPODA. 



Head separated from the segment which supports the second jaw-feet. Eyes sessile and im- 

 movable. Post-abdomen with narrow elongated swimming appendages below, which are 

 striated transversely, and furnished with cilia or hairs, and not with scales. Mandibles 

 furnished with a palpus. Body usually compressed, and curved underneath posteriorly. 

 Thorax usually divided into seven segments. Inhabits fresh and salt water. 



GENUS ORCHESTIA. Leach. 



The four anterior feet ending in a compressed claw ; that of the second pair being much 

 larger, its terminal joint long, arched, and applied to the sharp edge of the hand : this edge, 

 in the female, has a single tooth. 



Orchestia longicornis. 



PLATE rx. FIG. 28 & 28 a. Female. 



(STATE COLLECTION.) 



Talitrus (Orchcslia) longicornis. Say, Jour. Nat. Sciences, Vol. 1, p. 384. 

 Orchestia id. Gould, Invertebrata of Mass. p. 334. 



Description. Eyes oval. Lower antennae longer than the body ; the third joint, under the 

 lens, armed with series of short spines ; the fourth joint with about thirty articulations, 

 minutely spinous beneath. Second pair of feet with the hands dilated, oval, smooth, with 

 two obtuse spines on the anterior margin ; one at the lower angle, and the other more elevated 

 in the middle : the thumb much curved, acute at its tip, which rests on the interval between 

 the two tubercles (see fig. 28, a.). The two posterior pairs of feet longest. Upper pair of 

 antennae short, not extending beyond the second joint of the lower pair. 



Length, O'5-l'O. 



These small crustaceans are well known under the name of Sand-flea, or Beach-flea, 

 occurring along the shores of Long island, digging holes in the sand in which they conceal 

 themselves, and living upon dead animal substances. They furnish an abundant supply of 

 food to the numerous birds found along that coast. 



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