74 



projection issuing from inside the 2nd joint; those in male with the outer rami 

 more or less transformed and dissimilar, that of right leg, as a rule, the stronger. 

 Remarks. In the restriction here adopted, this family is chiefly charac- 

 terised by the structure of the legs, the 4 anterior pairs having both rami 

 3-articulate, and the last pair, at any rate in the female, being natatory, like 

 the preceding pairs. The strong unguiform projection always found inside the 

 outer ramus of the last pair of legs in the female is also very characteristic. The 

 family comprises as yet 5 genera, viz., Centropages, Kroyer, Isias, Boeck, Limno- 

 calanus, G. 0. Sars, Osphranticum, Forbes, and BoecJcella, Thomson. Of these 

 genera, the first 2 are exclusively marine, whereas the other 3 are chiefly peculiar 

 to fresh water. The first-named 3 genera are represented in the fauna of Nor- 

 way, and will be treated of below. 



Gen. 20. CentrOpagGS, Kroyer, 1848. 



Syn: Ichtyophorba, Lilljeborg. 



Generic Characters. Body moderately slender, with the cephalosome some- 

 what contracted in front, and having a well-marked cervical depression dorsally; 

 rostral appendages in some cases transformed to rigid spikes. Last segment of 

 metasome distinctly defined from the preceding segment, and having the lateral 

 parts, as a rule, expanded and acutely produced. Urosome in female more or 

 less asymmetrical, in male generally composed of only 4 segments. Caudal rami 

 of moderate length, with the setse comparatively short. Eye well developed, 

 subventral, and generally forming a distinct bulging below. Anterior antennae very 

 slender, consisting in female of 24 articulations, the last 2 joints being coalesced. 

 Posterior antennae with the outer ramus longer than the inner, and 6-articulate. 

 Anterior maxillipeds with the distal setse remarkably elongated, almost claw-like. 

 Terminal joint of outer ramus in the 3 middle pairs of legs with 3 spines outside. 

 Last pair of legs with the inner ramus well developed in both sexes and 3-arti- 

 culate ; outer ramus of left leg in male biarticulate, that of right leg 3-articulate, 

 the last 2 joints forming together a powerful chela. No ovisac present in female. 



SemarJcs. This genus was established as early as the year 1848 by 

 Kroyer, to include 2 species found by him, the one in the Atlantic Ocean, the 

 other off the coast of Chili. As first shown by Boeck, the genus Ichtyophorla 



