1901.] SOME ARCTIC XEMJERTEANS. 101 



As descriptions of these species are scattered over numerous papers, 

 it has seemed worth while to collect them into a list and to give in 

 each case a brief diagnosis based upon such characters as have been 

 shown to exhibit marked and definite divergences among the various 

 species (see Table facing this page). The details necessary for 

 forming a complete list are not forthcoming in all the species, and 

 the list has in part been made with the idea of drawing to such 

 omissions the attention of those who may be able to remedy them. 

 In the original description of some species the external appearance 

 alone has been chronicled. The names of such species are given 

 in a footnote at the bottom of the table. The species have been 

 tabulated according to their geographical distribution. In the 

 nomenclature of the marine regions the classfication suggested by 

 Ortmann ' has been followed. The species found in the North 

 Atlantic and in the Mediterranean are fairly well known, though 

 perhaps the region for which our knowledge is most accurate is 

 the North Pacific, owing to the recent publication of a valuable 

 paper by Coe '". With the exception of a few South-Georgian 

 forms described by Burger, we have practically no kuowledge of 

 the genus south of the Equator. Until our knowledge of Southern 

 and Tropical forms is somewhat more extensive, it is safest to 

 avoid any elaborate discussion on the affinities of the groups of 

 species inhabiting the various regions. A few points, however, 

 call for short notice. Numerous collections of Nemerteans have 

 now been worked out from the tropics — more particularly from 

 the Indian Ocean. A feature of such collections is the almost 

 total absence of species of Ampliiporus. As nearly all the species 

 of the genus are of fair size, often very plentiful, and readily 

 found where they occur, it would appear that they are relatively 

 scarce in the tropics, where their place is taken by the genera 

 Drepanophorus and Prosadenoporus. Whether the genus is well 

 represented or not in the South, it is not yet possible to say. The 

 few Antarctic species worked out by Burger are interesting when 

 compared with those from other regions. A careful examination 

 of the table will bring out the fact, that whilst the species of 

 Amphiporus inhabiting the Arctic circumpolar, the Atlantic boreal, 

 and the -Mediterranean respectively, show as groups considerable 

 amount of resemblance, they differ as much from the Pacific 

 boreal forms as these do from the Antarctic forms. In fact it 

 might be ■-aid that the Pacific boreal forms are more closely allied 

 to the Antarctic forms than to the North-Atlantic forms. In the 

 Pacific boreal and Antarctic forms, as compared with the ivsi , the 

 cerebral organ is mure often in front of the brain, the average 

 number of proboscis-nerves is a great deal higher (about 20 °/ ), 

 the number of reserve stylet-pockets is much more frequently 

 greater than two, and lastly there is a greater tendency for the 

 central stylet to be shorter than its base. That there should be 



1 Ortmann, A. E. : ' GTundziige der marineu Tiergeograpbie,' Jena, 1896. 



- Cor, W. It. : " I'api'i-s I'l-om the 11 .- 1 ■• i - i 1 1 1 ; i r i | Mil il !< »n : Tlio Nclut )'- 



leans," Proo. Wash. Anad. Bo. 1901. 



