83 



ought to be regarded as specifically distinct. It may be worthy of note in this 

 connection, that the present Calanoid is only found in the lowland lakes, never 

 at a height of more than 130 feet above the level of the ocean. 



Distribution. The great lakes of Sweden (Lilljeborg), Finland, and Russia 

 (Nordquist), as also those of North America (Forbes). 



Fam. 14. Diaptomidae. 



Characters. Cephalosome well defined from the 1st pedigerous segment, 

 with a more or less distinct cervical depression above, front unarmed, or carrying 

 below 2 soft appendages. Last segment of metasome with the lateral parts in 

 female more or less expanded. Urosome comparatively short, consisting in female 

 of 2 or 3 segments, in male of 5 segments. Caudal rami not much prolonged, 

 and carrying the full number of setae. Eye distinct, subventral. Anterior antennse 

 in female consisting of 25 articulations ; right one in male distinctly geniculate. 

 Posterior antennse with the outer ramus generally longer than the inner, and 

 distinctly 7-articulate. Oral parts on the whole normal. Posterior maxillipeds, 

 however, in some cases exceedingly powerfully developed. Legs comparatively 

 strongly built, inner ramus in 1st pair biarticulate, in the 3 succeeding pairs 

 3-articulate. Outer ramus of 1st pair of legs with the 2nd joint unarmed outside; 

 terminal joint of this ramus in the 3 middle pairs comparatively short, with only 

 a single spine outside. Last pair of legs in female not natatory, though distinctly 

 biramous, inner ramus, however, very small and simple in structure, outer ramus, 

 as a rule, 3-articulate, penultimate joint produced at the end inside to a strong 

 claw-like projection, terminal joint very small, in some cases obsolete. Last pair 

 of legs in male very asymmetrical, right leg much the larger, and carrying at the 

 tip a slender, movable claw. Ovisac present in female. 



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

 terised by the structure of the legs, and especially of those of the last pair in 

 both sexes, partly also by the shape of the urosome and the presence in the 

 female of a well-developed ovisac. It comprises exclusively inland forms, occurring 

 more generally in fresh-water lakes and ponds, but sometimes also in lakes 



