133 



division; genital segment (in female) with a lamellar, posteriorly-pointing expansion 

 on each side. Caudal rami short. Anterior antennae comparatively small and 

 resembling in structure those in the DyapontiidcB. Posterior antennae still smaller, 

 4-articulate, with the outer ramus rudimentary. Siphon well developed and rather 

 coarse, gradually tapered distally. Mandibles without any palp. Maxillae with 

 the lobes rather unequal in size. Both pairs of maxillipeds powerfully developed. 

 Natatory legs strongly incurved, with the rami subequal in length, and on the 

 whole built on the same type as in the Dyspontiidce, except that the 4th pair 

 is wholly wanting. 



Remarks. This genus was established as early as the year 1859 by 

 Boeck, to include a peculiar Copepod found by him on the south coast of Norway. 

 As only a solitary specimen was observed by that author, the generic characters 

 were not made out satisfactorily, and several errors were indeed introduced, 

 which however have partly been corrected by subsequent authors. The genus 

 comprises as yel only a single species, to be described below. 



74. Artotrogus orbicularis, Boeck. 



(PL LXXVIII). 



Artotrogus orbicularis, Boeck. Tvende nye parasitiske Krebsdyr; Chr. Vid. Selsk. Forhandl. f. 1859, 



p. 171, PL I, figs. 110. 



Specific Characters. Female. Body pronouncedly clypeiform, and nearly 

 orbicular in outline, with the dorsal face evenly vaulted, the ventral flattened or 

 concaved. Cephalic segment very large, occupying rather more than half the 

 total length, and having the free edges evenly arched; postero-lateral corners 

 triangularly produced and curved backwards; frontal part scarcely prominent and 

 without any dorsal crest; rostral prominence imperfectly defined and blunted at 

 the end. Epimeral lappets of the 2 succeeding segments large and recurved. 

 Tail extremely short, being almost wholly received within the deep emargination 

 formed behind between the epimeral lappets of the 2nd free trunk-segment; 

 genital segment sub- quadrate in form, and produced on each side behind to a 

 narrow lamella flanking the 2 succeeding very short segments; anal segment 

 larger than those segments combined and somewhat widening distally. Caudal 

 rami scarcely longer than they are broad, and rather wide apart, outermost 

 seta at some distance from the end and about the length of the innermost; the 

 2 middle setae not much produced. Anterior antennae scarcely attaining in length 

 1 /s of the cephalic segment, and composed of 9 joints clothed with moderately 

 long setae, 1st and 3rd joints the longest; terminal joint club-shaped and about 

 the length of the 2 preceding ones combined; the aesthetask, attached to this 



