Section 1. 



Amphaseandria. 



This section is chiefly characterised by the fact that both of the anterior 

 antenna 1 in the male are alike and only slightly transformed, never exhibiting any 

 geniculate structure, but only differing from those in the female by a more or 

 less pronounced coalescence of some of the articulations, and in the much more 

 abundant supply of sensory appendages. In the greater number of genera the 

 adult male is moreover distinguished by a very conspicuous transformation of 

 the oral parts, some of which appear greatly reduced. In some cases also the 

 external appearance of the male is so very different from that of the female, that 

 it becomes rather difficult to recognise both as belonging to the same species. 



All the Amphaseandria, as yet known, are marine, and by far the greater 

 number lead a true pelagic life, though there are a few forms that seem to be 

 more restricted to the bottom, being as yet only found close to the ground 

 in moderate depths, e. g. the species of the genera Undinopsis, Bryaxis and 

 Pseudophaenna. On the other hand, some of the forms, e. g. Paracalanus parvus, 

 are almost constantly found at the very surface of the sea, and are often thrown 

 by the waves upon the shore, where they may be found in considerable numbers, 

 left in tidal pools. 



The Norwegian forms belonging to this section may be referred to 8 

 different families, of which diagnoses are given below. 



