INTRODUCTION. 



Under the head Cydopoida I comprise a number of Copepoda, which on 

 the whole may be said to be built upon the type of our common fresh-water 

 fleas (Cyclops), though exhibiting many modifications, both as to their general ap- 

 pearance and to their habits, the latter affecting chiefly the structure of the oral 

 parts. The present group, or sub-order, exhibits some relations both to the 

 Calanoida and to the Harpacticoida, and also shows a certain approach to some 

 of the other sub-orders distinguished by the present author, especially to the 

 Notodelphyoida and the Caligoida, though the Cyclopoid type may always be 

 easily recognisable. Whereas the extensive group Harpacticoida by earlier authors 

 has generally been comprised within a single family, the Harpacticidos, several 

 families referable to the present sub-order were established very early, though 

 their real connexion under a common type has not been recognised. 



According to the system proposed by Dr. Giesbrecht, the Cydopoida, like 

 the Harpacticoida, should be included in the 2nd of his 2 primary divisions, the 

 so-called Podoplea. This very extensive and heterogeneous group has been divided 

 by that author into 2 sections, Isokerandria and Ampharthrandria, according to 

 the non-prehensile or prehensile character of the anterior antennae in the male, 

 each section comprising several families, which have been enumerated in his 

 recent work on the family Asterocheridce, p. 57. I am, however, by no means 

 prepared to adopt this classification, which appears to me quite artificial, like 

 the primary grouping of the Copepoda into Oymnoplea and Podoplea. In the 

 sense here adopted, the sub-order Cydopoida comprises families referred by Dr. 

 Giesbrecht partly to the Isokerandria and partly to the Ampharthrandria, whereas 

 other families included by that author in the latter section are wholly removed 

 as types of distinct sub-orders. One of these, the Harpacticoida, has been treated 

 of in the preceding volume, the 4 remaining sub-orders, Notodelphyoida, Monstril- 

 loida, Caligoida and Lernceoida, being reserved for the succeeding volumes of the 

 present work. 



l Crustacea. 



