Ill 



parts of last segment of metasome not expanded, though in some cases angular 

 at the tip. Urosome narrow and elongated, genital segment scarcely at all 

 protuberant below, anal segment slightly widening distally. Caudal rami flattened, 

 with the seta? comparatively short, one of them attached to the outer edge, at 

 some distance from the others. No special luminous organ present. Anterior 

 antennae conspicuously attenuated, with some of the proximal joints projecting 

 into small denticles, last joint very small, but well defined from the preceding 

 one, which carries anteriorly an unusually long and slender bristle; prehensile 

 antenna of male (generally the left) with the sensory appendages of moderate 

 size and uniform appearance. Posterior antennae with the outer ramus scarcely 

 longer than the inner, and 6-articulate. Anterior lip somewhat prominent, and 

 defined in front by a slight sinus. Posterior maxillipeds very slender, with the 

 terminal part 5-articulate and longer than the 2nd basal joint. Inner ramus of 

 2nd to 4th pairs of legs about half the length of the outer, its terminal joint 

 with 2 setse on the outer edge. 1st joint in 2nd pair with strong hamiform pro- 

 cesses inside; outer ramus of these pairs moderately dilated, with the apical 

 spine well developed and finely denticulate on the outer edge; its 1st joint in 

 3rd pair somewhat larger than in the other pairs, and having a small incision 

 at the end outside. Last pair of legs in female 3- or 4-articulate, with slender 

 setse at the tip; those in male 5-articulate and more or less strongly incurved, 

 right leg with the terminal joint but slightly dilated, antepenultimale joint, as a 

 rule, with a slender spiniform process inside. 



Remarks. This genus was established in the year 1864 by Boeck, to 

 comprise 2 Norwegian species, and its near relation to the genus Pleuromma of 

 Glaus (= Pleuromamma, Giesbr.) was at the same time mentioned. The chief 

 distinction between these 2 genera consists in the presence or absence of a 

 special luminous organ, the latter being constantly found in the genus Pleuro- 

 mamma, whereas in Metridia no such organ exists. In addition to this character, 

 some other differences may, on a closer comparison, be demonstrated to exist, 

 justifying the separation of these 2 genera, the more so as several species of 

 each of them have been found. We know at present no less than 9 species 

 referable to the present genus, 2 of which belong to the Norwegian fauna and 

 will be described below. 



