seen specimens of every valid species hitherto established 

 in the whole literature. Finally it may be pointed out, 

 that a good number of the species established here and in 

 my earlier papers had been seen by earlier authors but 

 were not recognized, being mixed up in one way or ano- 

 ther or wrongly named, consequently the number of 

 species seen only by me is considerably lower than the 

 number established as new in my papers, and this increa- 

 ses the probability that comparatively very few species of 

 the world's fauna are still undiscovered. 



It may be mentioned, that it is a more close examina- 

 tion of the antennulas and above all the investigation of the 

 male copulatory organs as attempted in the « Siboga » 

 report which helped me to separate the real species with 

 so much certainty that I feel confident as to the results, 

 thinking that a personal conception as to the limitation of 

 species is now nearly or totally out of question. 



The aim of the present treatise is to give an enumera- 

 tion and a kind of abridged view of all genera and species 

 of the order, with short preliminary descriptions of the 

 new species and of some closely allied, already established 

 forms, the diagnoses of which were imperfect or incorrect 

 in points of importance. Furthermore notes on other 

 species, some analytical keys and divisions into groups 

 are added together with observations on sexual differences, 

 etc. In order to avoid unnecessary reiterations the descrip- 

 tions of several genera and of a good number of species in 

 the literature are deemed sufficient for my present pur- 

 pose, and I confine myself to references to the paper 

 most essential as to the animals in question. Very brief 

 statements on the distribution of numerous species are 

 added, but an exhausting account of this topic would 

 occupy too much space. A few remarks on synonymy are 

 given, but as to this topic and the cancelling of some 

 names for other reasons my « Siboga » report together 

 with Dr. Zimmer's Schizopoden (1909) contain nearly 

 exhausting statements ; it may be added here that Thysa- 



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