The greater number of the Ostracoda are of rather small size, the average 

 length of the shell only seldom exceeding a pair of millimeters. The largest 

 forms are found among the Cypridinidce (Gigantocypris) and the freshwater 

 Cypridae (Megalocypris). 



Ostracoda are found abundantly both in fresh waters and in the sea. But, 

 whereas the freshwater forms on the whole show a rather uniform appearance, 

 being almost exclusively referable to a single family (the Cypridae), the marine 

 Ostracoda are much more varied, exhibiting several very distinct types. As to 

 habits, some of the marine forms (Conchoeciidae) lead apparently a true pelagic 

 existence; but the great majority of Ostracoda are to be regarded as bottom- 

 animals, many of them (Cytheridae) being even quite devoid of swimming 

 faculty. We have not full evidence of the existence of true parasitisme within 

 the present order. 



As the shell of most Ostracoda is of a rather firm consistency and in 

 many cases is even strongly calcareous, this part of the animal admits of being 

 rather well preserved also in the fossil state. Indeed, numerous species of 

 Ostracoda have been recorded from almost all fossiliferous formations even up 

 to the Cambrian period, though the true systematic relationship of the oldest 

 genera (Primitia, Leperditia, Beyrichia), by our want of knowledge to the 

 anatomical details, may be regarded as somewhat doubtful. 



As to the systematic arrangement of the Ostracoda, at first only a restricted 

 number of families were established, to comprise the known genera, 3 such 

 families being proposed in 1850 by Baird in his well-known work, viz., Cypri- 

 dinidce, Cypridce and Cytheridce. The first attempt to a more exact systematic 

 grouping of the Ostracoda was made in the year 1865 by the present author 1 ), 

 who proposed to divide the order into 4 principal groups or suborders, each 

 comprising one or more families. The arrangement proposed was as follow: 

 1. Myodocopa with the 2 families Cypridinidce and Conchoeciidce, 2. 

 C/adocopa with the family Polycopidce, 3. Platycopa with the family 

 Cytherellidce, and 4. Podocopa with the 2 families Cypridce and Cytheridce. 

 This classification has been sanctioned by most subsequent authors. G. W. 

 Muller has however in his work on the Ostracoda of the gulf of Naple suggested 

 that the 2 suborders Cladocopa and Platycopa should more properly be wholly 

 rejected, the family Polycopidce being referred by him to the Myodocopa and 

 the family Cytherellidce to the Podocopa. I think however that the argumen- 

 tation given at some length by the said author in support to this view may 



Oversigt af Norges marine Ostrncodcr. 



