sections, the metasome and urosome, the former carrying the natatory legs, 

 evidently answering to the pleopoda in the Malacostraca, whereas the latter never 

 carries any true appendages, and is terminated by the so-called furca or caudal 

 rami. The division anterior to the metasome may more properly be termed 

 the cephalosome, though very often confluent with the 1st segment of the 

 metasome. It carries, as a rule, 6 pairs of movable appendages, viz., the anterior 

 and posterior antennse, the mandibles, the maxillae, and 2 pairs of maxillipeds. 

 At about the middle of this division, below, the oral aperture occurs, in the 

 free-living forms bounded in front by a flap-shaped anterior lip and behind 

 by a bilobate posterior lip. These lips in some of the parasitic forms are pro- 

 longed into a sipho receiving the styliform masticatory parts of the mandibles. 

 A more or less pronounced reduction of the cephalic appendages may be observed 

 in the most degenerate parasites (Lernseoida) ; and even in one peculiar group of 

 free-living forms, the Monstrilloida, this reduction is so far advanced, that only 

 the anterior antennae are left, not even the slightest trace of either the posterior 

 antennae or any of the oral appendages being visible, at any rate in the adult state. 

 As to the classification of the Copepoda, the views of the several authors 

 differ considerably, according to the characters which have been selected as the 

 basis for the classification. The well-known classification of the Copepoda by 

 T. Thorell into 3 great divisions, Gnathostoma, Poecilostoma and Siphonostoma, 

 refers exclusively to the structure of the oral parts, and was at first much esteemed 

 by carcinologists. As. however, quite gradual transitions in the structure of the 

 oral parts between these 3 types have been found to exist, and moreover, by 

 accepting these groups, otherwise evidently nearly-allied forms would be sepa- 

 rated from each other in an unnatural manner, this classification cannot at present 

 be regarded as fully satisfactory. The establishment by Dr. Giesbrecht of the 2 

 great divisions, or sub-orders, Gymnoplea and Podoplea, is certainly more natural; 

 but these divisions do not nearly suffice for the comprising of all the Copepoda, as 

 they apparently relate only to the pelagic form examined by that author. Nor, I 

 believe, can the recent subdivision of the Copepoda proposed by Dr. E. Canu, 

 according to the structure of the female genital openings, into the Monoporodelphia 

 and Diporodelpliia, lay any claim to general acceptation. There are, I think, 7 

 distinct types among the Copepoda, which may indicate as many great divisions 

 or sub-orders. These types are represented by the following well-known genera : 

 Calanus, Harpacticus, Cyclops, Notoddphys, Monstrilla, Caligus and Lerncea. In 

 accordance herewith, 7 divisions are adopted in the present work, viz., Oalanoida, 

 Harpacticoida, Cyclopoida, Notodelphyoida, Monstrilloida, Caligoida and Lernceoida, 

 each comprising a number of distinct families, which may be referred to 2 or 



