CEPHALOPODA. 11 



openings between the pieces of the cowrie, when it is drawn 

 up into the canoe and secured. — LoweWs Edible IloUusks, 16'7. 



Most of the species of octopods and the Nautilus are littoral 

 in habit, and have thence been conjectured to enjo}" but a limited 

 distribution ; and this is held to justify the multiplication of 

 specific names. This reasoning is, however, fallacious, as it is 

 well known that many littoral mollusks, not nearly so well pro- 

 vided as these Avith the means of swimming, have become world- 

 wide in distribution. So man}' particular species of Octopus are 

 known to inhabit the shores of distant countries, that a large 

 proportion of the species which have been distinguished b}^ slight 

 and mutable characters, and b}^ their geographical distribution, 

 will probabl}' need to be united when sufflcientlj^ studied. This 

 probable extensive distribution of living littoral species corres- 

 ponds with observations made upon fossil species of Ammonites, 

 Nautilus and other chambered genera, which are proved to have 

 been littoral in habit hy their occurrence only in deposits repre- 

 senting ancient sea-shores. Not to multiply" examples amongst 

 these fossils, it may be mentioned that Nautilus simplex occurs 

 in Europe, East Indies and Texas ; that Ammonites Botomagensis 

 is found in Europe, East Indies, N. and S. Africa and S. America ; 

 and that Baculites anceps had even a wider distribution. Never- 

 theless, temperature has been observed to have some effect upon 

 the distribution of the living Octopoda of Europe, similar but 

 distinguishable forms or species inhabiting its northern seas, 

 from those of the Mediterranean. As in Molluscan life generally, 

 the development of specific forms has been greatest in tropical 

 waters. 



It is altogether probable that the pelagic cephalopods, highly 

 organized, with powerful locomotive apparatus, and frequently 

 attaining great size and strength, may enjoy a distribution fully 

 equal to that of the littoral species : such is known to be the 

 case in some species which, normally circumboreal in distribu- 

 tion, are found nevertheless extending into temperate latitudes 

 in both oceans. 



Order 1. Dibranchiata. — Breathing by a single pair of internal 

 symmetrical branchiae or gills. Ej^es sessile. Mandibles horny. 

 Arms, eight or ten, furnished with rows of acetabulse or suckers. 

 Body sometimes laterally or posteriorly finned. Shell internal, 

 or none. 



Order 2. Tetrabranchiata. — Breathing b}'^ two pairs of sym- 

 metrical branchiae. Eyes pedunculated. Mandibles shelly. Arms 

 very numerous, without suckers. Shell external, chambered ; 

 capable of containing the animal. 



