GAMMARrS. 329 



other rough surface, the dactylopodite being reduced to a 

 slightly curved spine. The pleopods move backwards and 

 forwards briskly, keeping up a stream of water which 

 washes the ventral surface of the body and the branchia? 

 which it bears. The first four thoracic feet and mouth 

 parts maintain a regular movement forwards, scooping up 

 water and food to the mouth. The uropods and telson, 

 and more rarely the antennae, are now and then drawn 

 through the thoracic feet, doubtless to free their hairs of 

 any particles adhering to them. Usually, the creatures 

 move along on their side, close to some surface ; by 

 pushing against this, the long clawed peraeopods thrust 

 the body forwards. The first four thoracic feet seem to 

 be of little use in progression, but the pleopods move 

 briskly backwards and forwards. If the animal is cross- 

 ing an open space, it swims rapidly by alternately flexing 

 and extending the abdomen, the last three segments of 

 which move together, so that it darts forward somewhat 

 spasmodically. When creeping slowly, it feels its way 

 with the long antenna?, the first pair being held out 

 horizontally in front, whilst the second pair are bent 

 downwards to touch the floor of the passage. The 

 antennae seem to be more used in the avoidance of obstacles 

 than the eyes are. 



In G. pule.v the colour is a dull greenish yellow or 

 brown, of variable shade. Brilliant spots of vermilion on 

 the abdomen and basal joints of the legs mark the position 

 of unicellular glands. The sexes are separate, the male 

 being distinguished from the female by its greater size 

 and stronger gnathopods, as well as by the absence of 

 oostegites on the first four thoracic legs. The adult male 

 is usually from 18 to 20mm. in length, the female from 

 10 to 12mm. 



In G. locusta the colour is somewhat variable, being 



