496 



fully 43 mm. The body is on the whole more strongly built, and has the 

 dorsal projections consideralily larger, and well defined also on the anterior 

 segments of the mesosome. The rostrum is very large, projecting considerably 

 beyond the basal joint of the superior antennae, and exhibits a distinct and 

 even cnrve. The superior antennte appear comparatively shorter, with the 

 flagellura but little lojiger than the peduncle. The anterior gnathopoda differ 

 rather conspicuously in their structure, being not nearly so strong as the 

 posterior, and having the propodos scarcely at all expanded distally, with the 

 palm much more oblique. The 3 posterior pairs of pereiopoda exhibit a 

 similar mutual longitudinal relation to that in G. relictus, but appear of 

 considerably stronger build, and less elongated Finally, the last pair of 

 uropoda is comparatively shorter. 



Occurrence. — The only place, where I have met with this form, is in 

 our largest lake, Mjosen, where a young specimen was captured, many years 

 ago, and described in my work: 'Histoire nat. d. crust, d'eau douce de 

 Norvege*. The specimen here delineated was found in Boeck's collection, 

 without however being accompanied by any statement of locality. Probably 

 it was also taken fi'om the lake Mjosen. 



DistriJyution. — The great lakes of Sweden (AYetter, Wener, stora 

 Lee), Finland, and Russia (Ladoga, Onega). 



Gren. 5. Gammarus, Fabr. 1776. 



Body more or less elongated and compressed, with the back, as a 

 rule, evenly rounded, not carinated, and the segments of urosome provided 

 above with fascicles of spines, Cephalon without any distinct rostrum, 

 lateral corners rather broad, postantennal ones distinct. Anterior pairs of 

 coxal plates of moderate size; 4th pair the largest, and distinctly eraarginated 

 in its upper jjart; the 3 posterior pairs comparatively small. Eyes well 

 developed, with dark pigment. Superior antennae generally longer than the 

 inferior, and provided with a well-developed accessory appendage. Inferior 

 antennae rather strongly built, flagellura in male often provided with calceolae 

 anteriorly. Oral parts normal. Gnathopoda distinctly subcheliform, and 

 more or less strongly developed, being always much more powerful in male 

 than in female. Pereiopoda, as a rule, not very much elongated, the 3 posterior 

 pairs nearly eqiial-sized, and having the basal joint lamiuarly expanded. 

 Branchial lamellae simple, pedunculated; incubatory lamellae comparatively 



