507 



grey, each segment with a more or less distinct transverse band of a dark 

 brownish green hue. Length of adult male 15 mm. 



Remarks. The present form is nearly allied to the arctic species, 

 P. cancelloides of Gerstfeldt, and was indeed identified with that species by 

 Prof. Loven. It is distinguished, however, by the far sligter developement of 

 the spiniform projections of the body, only those of the 2 anterior segments of 

 metasome being distinct. Moreover, the structure of the last pair of uropoda 

 is rather different. The Gammarus Kessleri of Dybowsky from the Baikal 

 Sea would seem to be this species. 



Occurrence. I have found this form rather plentifully in our largest 

 lake, Mjosen, in depths varying from 3 to 50 fathoms. It also occurs in 

 3 other Norwegian lakes, viz, Hurdalsjo, Storsje and Femsj0, as also in the 

 river Vormen. 



Distribution. The great lakes of Sweden, Finland and Russia, the 

 Baikal Sea (Dybowsky). 



Ren. 7. Melita, Leach, 1813. 



Syn. : Ceradocus, Costa. 

 Msera, Dana. 



Body more or less slender, with the segments of mesosome always 

 evenly rounded above, those of metasome and urosome sometimes produced 

 dorsally to dentiform projections. Cephalon without any distinct rostrum, 

 lateral corners rounded. Coxal plates of moderate size,|4th pair the largest, 

 and more or less emarginated posteriorly. Eyes distinct, though rather 

 small. Antennee of the very same structure in the two sexes, the anterior 

 ones very slender, and much longer than the inferior, accessory appendage 

 more or less developed. Oral parts normal. Gnathopoda rather unequal, the 

 anterior ones comparatively small, and alike in the two sexes, the posterior 

 ones much larger, and in male often enormously developed, approaching 

 sometimes to a cheliform character. Pereiopoda rather elongated, the 3 

 posterior pairs successively increasing in length, and having the basal joint 

 laminarly expanded. Branchial lamella simple; incubatory lamellse narrow. 

 The 2 anterior pairs of uropoda normal; last pair projecting considerably 

 beyond the others, and having the rami very unequal, the outer one rather 

 large and spinous, with the terminal joint obsolete, the inner very minute 

 and scale-like. Telson small, bipartite. 



