2 BRITISH COPEPODA. 



three) wart-like, setiferous processes. Second pair 

 sometimes foot-like, but mostly forming a strong pre- 

 hensile uncinate hand. First pair of feet mostly 

 (though not always) different from the following pairs 

 and converted into a prehensile apparatus ; second, 

 third, and fourth pairs adapted for swimming ; fifth 

 pair 2-jointed, foliaceous ; different in the two sexes, 

 the basal joint usually dilated and more or less embrac- 

 ing the smaller apical joint. Eyes as in Cyclops. 

 Heart wanting. Copulative organs in the female 

 symmetrical, in the male usually asymmetrical. Ovisac 

 in most cases single, rarely double. 



This family, according to the arrangement here 

 adopted, contains thirty-three genera* and eighty- one 

 species, and is therefore by far the largest of the nine 

 families coming within the range of the present Mono- 

 graph. The limits of the family are precisely those 

 adopted by Claus and Boeck, except that the group 

 erected by the former author into a separate family 

 under the name Peltididce are here (as also by Boeck) 

 included amongst the Harpacticidce. There is, in 

 fact, no important structural difference between the 

 two, the point relied on by Claus as distinctive being 

 the flattened form of the Peltididce, which is of no 

 great importance in itself, and is found in certain 

 species of some genrea (e. g. Thalestris), the normal 

 form of which is cylindrical. The cylindrical form, 

 with an abdomen not much narrowed, and not mark- 

 edly distinct from the cephalothorax, must, however, 



* Excepting Cylindropsyllus, which cannot at present be referred 

 with certainty to any family. 



