499 



9. Gammarus locusta, Linne. 



(PI. 1, PI. 176, fig. 1.) 

 Cancer locusta, Linne, System a Naturse, ed. 12, p. 1055. 



Syn. : Oniscus pulex, 0. Fabr. 



Garnmarus arcticus, Scoresby. 

 boreus, Sabine. 

 mutatus, Lilljeborg. 

 sitchensis, Brandt. 



Body of a similar form to that in the preceding species, though perhaps 

 somewhat less elongated. Cephalon much shorter than the first 2 segments 

 of mesosome combined, lateral corners angularly produced in front and defined 

 below by a rather slight sinus. Anterior pairs of coxal plates, especially in 

 female, considerably larger than in G. mar-inns, and nearly twice as deep as 

 the corresponding segments; 4th pair nearly as broad as they are deep, 

 posterior expansion obtusely truncated at the tip. Last pair of epimeral 

 plates of metasome considerably produced at the lateral corners, terminating 

 in an acuminate point, and having the posterior edge setiferous. Segments 

 of urosome each with a well-marked nodiform dorsal projection, armed with 

 from 3 to 5 small spines, and having on each side, at some distance from 

 these, a group of from 3 to 4 spinules. Eyes reniform in shape, not 

 nearly so narrow as in G. marinus, pigment black, with a chalky white 

 coating. Superior antennae in female not quite half the length of the body, 

 in male somewhat longer, 1st joint of the peduncle about as long as the 

 other 2 combined, flagellum twice the length of the peduncle, accessory 

 appendage rather fully developed, exceeding half the length of the peduncle, 

 and composed of about 8 articulations. Inferior antennse somewhat shorter 

 than the superior, with the flagellum about the length of the last 2 

 peduncular joints combined, and in male provided with distinct calceolse. 

 G-nathopoda in female rather small and somewhat unequal, the posterior ones 

 being very slender, with the propodos narrow oblong, and considerably longer 

 than the carpus; those in male much more strongly built than in female, and 

 very unequal, propodos of the anterior ones obpyriform, of the posterior, 

 much larger, and irregularly quadrangular in form, palm in both pairs very 

 oblique, and armed in the middle with a strong spine. The 3 posterior pairs 

 of pereiopoda comparatively more slender and elongated than in G. mar inn*. 

 and edged with fascicles of slender spines, basal joint of antepenultimate 

 pair produced at the infero-posteal corner to an acute point. Last pair of 



