115 



somewhat flattened, widening distally, and projecting on each side in a conspicuous 

 angular corner. Caudal rami comparatively smaller than in Metridia. Anterior 

 antennae resembling in structure those in the above-named genus, some of the 

 proximal articulations being produced as more or less conspicuous dentiform pro- 

 jections, generally wanting in male; left antenna in the latter as a rule geniculate, 

 and having the proximal sensory appendages very large, leaf-like. Posterior 

 antenna? with the outer ramus longer than the inner, and distinctly 7-articulate. 

 Anterior lip rather prominent and defined in front by a deep transverse sinus. Oral 

 parts scarcely differing in their structure from those in Melridia. Natatory legs, 

 on the other hand, much more strongly built, with the outer ramus of 2nd to 4ht 

 pairs very large and expanded, with comparatively short spines and seta?; that 

 of 3rd pair with a very deep incision at the end of the 1st joint. Inner ramus 

 in these pairs not attaining half the length of the outer, and having only a 

 single seta outside the terminal joint; that of 2nd pair with the 1st joint distinctly 

 hooked inside. Last pair of legs in female 2- or 4-articulate ; those in male 

 5-articulate, with the terminal joint of right leg securiformly dilated, and the 

 penultimate joint of same leg armed inside with a short spiniform process. 



Remark*. This genus was established by Glaus, to include the Diaptomus 

 abdominalis, Lubbock, and another Mediterranean species P. gracile, Cls.; but 

 as the generic name proposed, Pleuromma, had been previously appropriated in 

 Zoology, Dr. Giesbrecht has recently changed it to Pleuromamma. This change 

 becomes the more necessary, as the organ regarded by Glaus as an eye, has 

 turned out to be of a very different nature, being undoubtedly, as first suggested 

 by Dr. Dahl, a special luminous organ. The genus is very nearly related to 

 Metridia, though differing not only in the presence of the above-named organ, 

 but also in some other features mentioned in the above diagnosis. We know at 

 present of 6 species of this genus, one of which belongs to the fauna of Norway, 

 and will be described below. 



50. Pleuromamma robusta (Dahl). 



(PI. LXXVIII & LXXIX). 

 Pleuromma robust in, F. Dahl in ,,Zool. Anzeiger"', Vol. 16, p. 105. 



Specific Characters. Female. Body, as compared with the other species, 

 somewhat robust, with the anterior division, seen dorsally, oblong oval in form, 

 greatest width exceeding a / 3 of the length, and occurring a little behind the 

 middle, anterior extremity somewhat contracted and triangularly produced at the 

 tip, posterior only slightly attenuated. Gephalosome not attaining the length of 



