INTRODUCTORY REMARKS. 179 



consideration ought to be pointed out. In the Syn()p.sis inoiitioiieci (1!)11) 

 I set forth several reasons for the belief "that comparatively few, probably 

 not a dozen, species in the oceans of the globe are still undiscovered." And if 

 that view be correct it must be admitted that the results of the Agassiz explora- 

 tion in 1904-1905 are as to this order of Crustacea wonderfully rich, because 

 during that trip thirty-nine species were collected, thus a little more than half 

 of the species hitherto known — and not far from half of the species really 

 existing!— The collection contains besides a large number of larvae, of Euphau- 

 siacea, but on this topic it may be sufficient to refer to my remarks in the 

 chapter on the larval stages (p. 283-294). 



As to the classification of the Mysidacea and some characters in the Euphau- 

 siacea — especially the important copulatory organs of first pair of pleopods 

 in the male — I may refer to the account in my paper on the "Siboga" Schizo- 

 poda frequently quoted on the following pages. Only a few points may be 

 added. Recently I found that in some genera (Thysanopoda, Nematoscelis, 

 and Nematobrachion) the maxillulae afford valuable specific characters or 

 characters for groups of species belonging to the same genus, furthermore that 

 in a few genera the maxillae show specific differences of some interest, finally 

 that in the genus Nematoscelis the thoracic legs afford excellent characters for 

 dividing the genus into two natural groups. — The nomenclature of the cepha- 

 lothoracic appendages in the two orders is identical with that applied in the 

 "Siboga" paper. 



The geographical distribution of each species is mentioned. I have at- 

 tempted in all cases to give a full abstract of all trustworthy statements in the 

 literature, but as to several species of various genera (Euphausia, Nematoscehs, 

 Stylocheiron) most of the earlier statements had to be discarded as the species 

 in question were "collective." I have added a good many statements based 

 on the material of the Copenhagen Museum, but do not think it well to insert 

 still unpublished results based on collections to be reported on in the near 

 future, namely those from the Swedish Antarctic Expedition, from the U. S. 

 National Museum, etc. 



And now I may express my deep regret that Dr. A. Agassiz did not li\-e 

 to see the publication of this paper, because it would certainly have been a 

 satisfaction for that great explorer to see how rich his collection of these groups 

 of Crustacea and especially of the oceanic Euphausiacea in reality was and 

 how important it proved for the advancement of this branch of zoological 

 science. 



