A Catalogue of Recent Cephaloiwda,. 207 



genera ; lience it may be said in round numbors that we are 

 acquainted with 50 or 60 genera of recent Cephalopoda con- 

 taining 300 species. It is worthy of remark that 29, or half 

 the genera, contain only one species each, while nearly one- 

 half the species, 170, belong to the three genera Octopus, 

 Se2na, and Loligo. 



As regards their distribution the Cephalopoda seem to be 

 divisible into three groups — (1) the Pelagic, (2) the Abyssal, 

 and (3) the Littoral. 



The first two of these have been united under the name 

 " Oceanic " species, and have been disposed in three groups 

 corresponding to the Atlantic, Pacific, and Indian (including 

 the Southern) Oceans, rather for convenience than from a 

 belief that such a division is natural, although the great 

 majority are confined to one area. The chief factor limiting 

 their spread is probably temperature, though doubtless other 

 conditions, such as the presence of Gulf weed, also have their 

 influence. 



The " Littoral " species, that is, those found in moderately 

 shallow water not far from the coasts, whether they be active 

 swimmers like Loligo, or more sedentary like Octopus, are 

 much more restricted in their range than the oceanic. For 

 the purpose of representing their distribution, the coasts of 

 the world have been divided into seventeen regions, which 

 are very different in extent and in the number of species 

 that have been recorded from them. As regards the former 

 of these points it may be remarked that no sharp boundaries 

 can be drawn between them at all ; for, although for statis- 

 tical purposes it may be necessary to adopt lines of demarca- 

 tion, these are not recognised by nature, and, furthermore, a 

 fuller knowledge of the faunas of the various regions would 

 almost certainly show that some of the districts here proposed 

 should be subdivided and others united. 



The geographical regions here adopted agree very closely 

 with those proposed by Dr Paul Fischer in his recent 

 Manual,^ based upon a study of the whole of the MoUusca ; 

 their names and boundaries are as follows : — 



1. The Scandinavian Region includes the whole of the 



^ Manuel de Concliyliologie, 8vo, Paris. 



