THE SCHIZOPODA OF THE SIBOGA EXPEDITION 



BY 



H. J. HANSEN, 



Copenhagen. 



With 16 plates and 3 text figures. 



INTRODUCTORY REMARKS. 



The material of Schizopoda collected by the "Siboga" Expedition is large. But when 

 we wish to get a more special view it is necessary to consider separately the two orders still 

 generally put together under that name, viz. the Mysidacea and the Euphausiacea. 



The large majority of the Euphausiacea are true oceanic forms, living generally either 

 in the upper layer from about 100 metres to the surface or in more considerable depths; only 

 very few inhabit as a rule shallower water either near land or at most at a distance of some 

 miles from the coast. The major part of the stations of the "Siboga" are situated close by 

 or not very far from the coast of one of the innumerable islands of the Indian Archipelago, 

 consequently the number of Euphausiacea captured is moderate, comprising 25 species, 7 (8) 

 of which are new. That the number of new forms is even so high is due to the fact that I 

 have been able to separate with certainty species hitherto confounded with each other or over- 

 looked, and this was done by a more special investigation of the copulatory organs of first pair 

 of pleopods in the male sex. These organs have been completely omitted by previous writers 

 excepting G. O. Sars, and this eminent Zoologist produced a number of figures of these very 

 complex organs, but in reality did not perceive their extreme importance, did not see that in 

 most genera they present the most reliable characters for the separation of species otherwise 

 closely allied or even scarcely distinguishable. Five of these new species are known to me from 

 other oceans, most frequently from the Pacific; Eitphausia Siboga? H. J. H. has been mentioned 

 by me from Amboina, but of Stylocheiron affine n. sp. and S. insularc n. sp. only the "Siboga" 

 specimens have been seen. 



SIBOGA-EXPEDITIE XXXVII. I 



* 797 



