334 INVERTEBRATA OF MASSACHUSETTS. 



erect. Some of them live almost entirely out of the water, and 

 may be at any time found under stones and sea-weed along the 

 sea-beach. Their leaps are effected principally by the append- 

 ages to their tails, which they bend underneath them, and by sud- 

 den extension toss the body with surprising force. They depend 

 for subsistence on dead animal substances which the waters float 

 to them. 



It is very difficult to make out the different species, or even to 

 determine the genera. The species of the European side of the 

 Atlantic are too briefly described and too badly figured to enable 

 one to be certain what species are common to both shores ; so 

 that I am not fully satisfied with the following results. 



GENUS ORCHESTIA, LEACH. 



O. LONGICO'RNIS. Talitrus longicornis, SAY; Journ. Acad. Nat. Sc., 

 i. 384. 



This appears to be the same as Cancer gammarus saltator of 

 Montagu, (Trans. Lin. Soc., ix. 94, tab. 4, f. 3,) which is given 

 as synonymous with Talitrus locusta of Lamarck, Pennant, and 

 others. But it is not Gammarus locusta of Montagu. 



O. GRYLLUS. Talitrus gryllus, Bosc ; Hist. Nat. des Crust., ii. 104. 

 SAY; Journ. Jlcad. Nat. Sc., i. 386. 



The following seem to be synonyms, viz. 



Talitrus gamarellus, LATR. and LAM. Orchestia littorea, LEACH; Trans. Lin. 

 Soc., xi. 356. DESM. ; Consid., <^c., 261, pi. 45, f. 3. 



GENUS GAMMARUS, FABR. 



G. LOCU'STA, MONTAGU; Lin. Trans., ix. pi. 4, f. 1. MILNE-DW. ; Ann. 

 des Sc. Nat., xx. 367. 



This is not G. locusta of Pennant, Gmelin, Pallas, and Fabri- 

 cius, which is a Talitrus. 



G. MINUS, SAY ; Journ. Acad. Nat. Sc., i. 576. 



Found in ditches and sluggish fresh water, adhering to sticks. 



Two or three other species of ORCHE'STIA, and one of AM- 

 PHI'THOE, remain undetermined. 



