5 



separated from tlie rest ol the shield h}' an imperfect 

 hinge, and enclose below a very deep sinns. Like the 

 rest of tlie animal, the cephalothorax is flattened laterally. 

 It bears the eyes, the first and second antennae, the 

 mandibles, the first and second maxilla^, and the niaxilli- 

 peds, which belong" to the fused first segment of the 

 thorax. The mouth (PI. II., m.) opens from out of the sinus 

 between the lateral plates of the ceplialothoracic shield. 

 In front it is protected by a small labrum, divided into 

 an upper and lower part by an imperfect hinge, and 

 fringed with numerous seta'. It is guarded at the sides 

 b}' the scoop-like projections of the mandibles (PI. I., fig. 

 4), and behind l)y the maxillipeds, the basal joints of 

 which are fused, bo that they form a lower lip (PI. I., fig. 

 7). The excretory organ opens on the el(»ngated tip of 

 the antennary cone (PI. II., rmf. c), on the basal joint of 

 the second antenna. The eyes (PI. I., tig. 15) are com- 

 pound, sessile and reniform, the posterior margin being 

 convex. The corneal cuticula, as Leydig (11) noted, is 

 smooth and without facets. 



The thorax consists of eight segments, of which the 

 first, bearing the maxillipeds, is fused with the cephalon ; 

 the remainder are free. The seven free segments (PI. II.) 

 bear each a pair of legs, which normally carry branchia? 

 on the inner side of their basal joints, though in some 

 cases these are absent from the first pair. The first foiir 

 bear legs directed forwards and carrying enlarged coxal 

 plates (PL II., c.p.) which gradually increase in size horn 

 the first to the fourth segment, the last being notched in 

 the upper part of its posterior edge to give play to the fifth 

 leg. These coxal plates are of moderate size compared 

 with those of some other species of Gammarus. They are 

 somewhat larger in G. locusta than in G. index. They 

 function as accessory respiratory organs, being covered on 



