The oral parts, as mentioned above, are of very different structure in 

 the 3 sections of Cyclopoida. 



The natatory legs are, as a rule, shorter and stouter than in the Har- 

 pacticoida, with the basal part broad and flattened and the rami generally well 

 developed and subequal in size. The 1st pair are smaller than the succeeding 

 ones and never prehensile. In a few of the parasitic forms, for instance Cancerilla, 

 a considerable reduction of the natatory legs is found to have taken place, at 

 least in the female. 



The last pair of legs are always very small and simple in structure, 

 being in most cases exactly alike, in the two sexes. 



The ova are carried in 2 ovisacs, which are lateral or even subdorsal, 

 never, as in the Harpacticoida, ventral. Only in one instance, viz., in our in- 

 digenous species of Corycceus, have I found only a single ovisac, which, however, 

 is attached quite dorsally. 



The Cyclopoida are well represented also in fresh water by numerous 

 species of the genus Cyclops and allied forms, and some of the parasitic forms, 

 for instance Ergasilus, are also true fresh-water animals. 



Section 1 Gnathostoma. 



General Characters. Anterior antennae in male distinctly hinged. Posterior 

 antennae without any outer ramus, and carrying on the tip a number of curved 

 setae. Oral parts adapted for mastication. Masticatory parts of mandibles and 

 maxillae strongly dentate. Maxillipeds not subchelate; the posterior ones smaller 

 than the anterior, and of the same appearance in the two sexes. Natatory legs 

 well developed, with both rami generally 3-articulate. 



Remarks. The several forms belonging to this section have generally 

 been combined within a single family, the Cyclopidw. It is, however, very easy 

 to distinguish at least 3 well-defined families of gnathostomous Cyclopoida. All 

 these 3 families are represented in the fauna of Norway, and will be shortly 

 characterised below. 



