592 



7. Ischyrocerus megacheir, (Boeck). 



(PI. 211). 

 Podocerus megacheir, Boeck, Crust, amph. bor. & arct. p. 187. 



Body comparatively slender and rather compressed. Cephalon some- 

 what exceeding in length the first 2 segments of mesosome combined, and 

 having the frontal part rather produced, lateral lobes acutangular. Coxal 

 plates scarcely deeper than the corresponding segments; 1st pair angular in 

 front; 4th pair scarcely larger than the 3rd; 5th pair with the anterior lobe 

 nearly as deep as the preceding pair. Last pair of epimeral plates of meta- 

 some rectangular. Eyes rather large, rounded oval, pigment light brown. 

 Antennae very much elongated and densely setiferous ; the superior ones equal- 

 ling about 2 /3 of the length of the body, and with the last peduncular joint 

 the longest, flagellum in female about half the length of the peduncle, and 

 composed of 8 articulations, in male somewhat longer, and 10-articulate. 

 Inferior antennae about the length of the superior, last joint of the peduncle 

 the longest, flagellum half the length of the peduncle and 8-articulate. 

 Grnathopoda of female somewhat unequal, the posterior ones being considerably 

 larger than the anterior, propodos in both pairs regularly oval in form, with 

 the palm imperfectly defined; the posterior ones in male extremely powerful, 

 with the propodos very large and tumid, exhibiting an oblong oval form, 

 palm slightly flexuous, with a low, irregularly crenulated prominence in front, 

 and defined posteriorly by an obtuse angle carrying several small spines, 

 dactylus very strong and, when closed, impinging with the tip somewhat 

 inside the palmar edge. Pereiopoda much more slender than in the preceding 

 species, the 3 posterior pairs successively increasing in length, and having 

 the basal joint oblong oval in form, with the hind edge smooth. Last pair 

 of uropoda with the rami subequal, the inner one but slightly hooked at 

 the tip, with a single small spine at about the middle of the upper edge. 

 Telson subtriangular, about as long as it is broad at the base, and having 

 2 slender unequal bristles on each side of the tip. Body whitish, pellucid, 

 with light orange bands across the segments. Length of adult female 7 mm, 

 of male ii mm. Maximum length of Arctic specimens 12 mm. 



Remarks. The present species, first established by Boeck, is easily 

 distinguishable by the slender form of the body, the very much elongated and 

 densely setiferous antennae, the structure of the gnathopoda in the 2 sexes, 

 the slender form of the pereiopoda, and the absence of secondary hooks on 

 the inner ramus of the last pair of uropoda. 



