GAMMARUS. 337 



larger than that of the first, and in the female both are 

 smaller than in the male. They are armed with short, 

 stout spines on the lower or posterior edge, on which the 

 strongly-clawed dactylopodite shuts down like the blade 

 of a knife, so that they are sub-chelate. Both gnathopods 

 are thickly beset with seta?, especially on the lower edge, 

 and both bear an enlarged coxal plate (PL I., fig. 9, c.p.) 

 and internally a branchia (PL I., fig. 9, br.) on the 

 coxopodite. In some specimens examined, the branchia 

 was absent from the first gnathopod. 



The first and second perasopods (PL I., fig. 10) are very 

 similar. The coxopodite bears externally a coxal plate, 

 and internally a branchia (PL I., fig. 10, c.p. and br.) as 

 in the gnathopods. The basipodite is long, and the 

 meropodite is provided with two very strong spines, the 

 dactylopodite being reduced to a strong, movable claw. 

 The whole appendage bears a row of long seta? on its 

 lower or posterior margin as well as fascicles at the joints. 



The last three peraeopods (PL II., per. 1, 2, 3) are 

 similar to one another. The coxopodite which bears a 

 branchia on its inner side is short and broad, the basi- 

 podite being elongated, broad and flat, and the ischiopodite 

 small. The dactylopodite is reduced to a strong, movable 

 claw, and the other three joints are all long and slender, 

 bearing fascicles of seta?, and are usually carried bent 

 upwards from the ischiopodite, so that their tips extend 

 above the dorsal line of the animal. The last one is the 

 longest. They are more slender and elongated in G. pulex 

 than in G. locusta. In G. locusta the basal joint of the 

 antepenultimate pair is produced at the infero-posteal 

 corner to an acute point. The creature aids itself in 

 creeping along by thrusting these long, clawed pereeopods, 

 turned up over its sides, against any rough surface. 



The pleopods (PL I., fig. 12, PL II. pi. 1,2,3) consist 



