160 THE VOYAGE OF H.M.S. CHALLENGER. 



From the tables I may also deduce a list of abyssal genera, which is as follows : — 



Munnopsis.*^ 

 Eurycope.*^ 



1 Acanthocope. 

 Arcturus.*\ 

 Glyptonotus.*f 

 Astacilla.*\ 

 Stenetrium*f 

 Janira.*\ 



2 Anuropus. 



3 Bathynomus. 

 Serolis.*^ 

 Ischnosoma.*^ 



4 Acanthomunna. 



5 Trichopleon. 



Nannoniscus* 



6 Iolanthe. 

 Paratanais.*f 

 Typhlotanais.*^ 



7 Sphyrapus (?) 

 Cryptocope.*^ 



8 Neotanais. 



9 Leiopus. 

 Paranthura.*f 

 Cymodocea*\ 

 Anceus.*f 

 Neasellus* 



The above list includes all those genera that are found in depths of 500 fathoms and 

 more. Those that are marked with an asterisk (*) are also found in the continental zone, 

 while those to which a dagger (t) is appended are found in the littoral zone. It appears, 

 therefore, that the nine numbered genera are, as far as at present known, absolutely con- 

 fined to deep water. This table, however, does not indicate those genera that are character- 

 istically abyssal, that is those in which the majority of species inhabit the greatest depths ; 

 Ischnosoma is characteristically a deep-sea form; only one species (Ischnosoma bispinosum) 

 is found in shallow water up to 300 fathoms; the remaining four species are all inhabitants 

 of very deep water. In the genus Eurycope about one-half of the known species are 

 abyssal; two of the four species of Munnopsis are abyssal, and very nearly all the species 

 of the genus Arcturus. On the other hand, Cymodocea, Astacilla, Stenetrium, Janira, 

 Paranthura, Typhlotanais, Cryptocope, and Paratanais are genera which are almost 

 exclusively confined to the littoral area, one species only of each (two of Typhlotanais) 

 descending into the great depths; of the remaining genera, Glyptonotus and Nannoniscus, 

 only two species of each are at present known, so that it is hardly worth whde drawing 

 attention to the fact that they are equally distributed in the greater and lower depths. 

 Anceus has two abyssal species and a very large number of shallow-water forms ; of 

 Serolis four species (25 p. c.) range into the abyssal waters. 



The only species known to me which are common to the abyssal and littoral region 

 are — 



Arcturus fur catus, a few fathoms and 1675 fathoms, 

 Bathytanais bathybrotes, a few fathoms and 2050 fathoms, 



though as already mentioned a great number of species are common to the littoral and 



