CRUSTACEA FROM THE « CHALLENGER ' EXPEDITION. 45 



unite these with the families of the shallow-water forms, and would suggest for the 

 Schizopods the following systematic arrangement : — 



9 abdominal segments, 8 legs I. Nebaliid^:. 



{6 legs II. Mysid-e. 



8 legs III. ETJPHATTSIIDJ3. 



41e|s IV. Chalaraspid*. 



7 legS V. LoPHOGASTRIDiE. 



In order to expose the genealogical connexion between the genera of these families, 

 it would he necessary to prepare a large table ; but I think that their relations will be 

 well understood from what I have said about the subject in the preceding pages, as well 

 as from a comparison of my plates with the figures given on the other genera by Sars, 

 Claus, and other authors. 



Two questions will arise, of course, from a comparison of the deep-sea forms with the 

 shallow-water forms : — (1) Are there no Schizopods in' the depths which show tbe 

 ordinary conformation of a shield fastened to the pereion ? and (2) As the Mysidse and 

 Lophogastridse have relations of very extraordinary characters living in tbe deep sea, 

 are there no forms which represent the third of the hitherto acknowledged families — the 

 Euphausiidse ? These questions are partly answered by the discovery of a very large 

 member of this family, which came up in the trawl in lat. 35° 41' S., long. 20° 55' W., 

 from a depth of 1900 fathoms. This animal is a male, has a length of 84 millims., and 

 belongs to Dana's genus Euphausia ; for its dorsal shield is 'perfectly fastened to the 

 pereion, and of the eight pairs of legs only six are developed, the last two being only 

 represented by the branchial appendages and the palpi. But, unlike all other species 

 of Euphausia hitherto known, it has no accessory eyes. There are very long olfac- 

 tory hairs on the enlarged first antennse, and the peculiar appendages to the pleo- 

 poda which characterize the males of this genus. I shall figure and describe this 

 species, which I intend to call Euphausia simplex, n. sp., when we come home, and 

 when it will be possible to compare it with the other species of the genus (which have 

 been described by Dana and Claus). Erom the discovery of this Euphausia, it appears 

 that not all the deep-sea Schizopods offer the said peculiarity, and that, among very 

 peculiar genera such as have been described above, a form is also to be found which 

 differs from the svirf&ce-Euphausice only by the absence of accessory eyes. These, I 

 think, are to be considered a secondary adaptation to pelagic life ; and therefore E. sim- 

 plex is probably a more ancient form than E. Mulleri, splendens, and superba. Probably, 

 however, this will not be the last discovery we make in this interesting group ; and I 

 think it is very likely that a form will come up which is in the same relations to the 

 Euphausiidse as Gnathophausia is to the Lophogastridse, and Petalophthalmus to the 

 Mysidae. Then we should have made one step forward in the knowledge of Schizopodal 

 genealogy, a step which will probably lead to further discoveries concerning the rela- 

 tions of the Phyllopods to the Schizopods — of the lower to the higher crustaceans. 

 Perhaps it will now also be possible to understand certain fossil forms which seem to 

 be allied to Nebalia and to Gnathophausia. 



