216 NATURAL HISTORY OF OUR SHORES 



the Pteropoda (or " Sea -butterflies "), for they also are 

 Cephalopodous, but this point in classification is another 

 of those on which doctors differ, and as the sea -butterflies 

 belong to the ocean rather than to the shore we can pass 

 on to the undisputed members of the class. The class is 

 divided into two orders, thus : 



ORDER 1. Tetrabranchiata (four gills). One genus 

 only of this order lives at the present time. This is the 

 Nautikis. 



ORDER II. Dibranchiata (two gills). 



Order II. is again divided as follows : 



SUB- ORDER I. Octopoda (with eight arms). Examples : 

 the common Octopus and the Eledone of our shores, and the 

 Argonaut of southern seas. 



SUB-ORDER II. Decapoda (with ten arms). Examples : 

 the so-called squids i.e. Sepia, Loligo, Ommatostrephes, 

 and Sepiola of our seas, and many examples in foreign 

 waters. The best known of all these is the common 

 squid (Sepia officinalis, Fig. 98). 



On the British coasts this is somewhat erratic in its 

 occurrence, occasionally arriving in large numbers, then 

 being absent for many years. On the southern side of the 

 Channel, including , the Channel Islands, it is constant 

 during the summer months. 



Much has been written about the octopus, from sensa- 

 tional, and generally very wild, newspaper paragraphs to 

 the most elaborate details of its anatomy in books of 

 science. But as regards its appearance and its habits 

 nothing, to my knowledge, has been so far attempted. 



The specimens that occur in these seas are, when full 

 grown, of about eight feet in spread of arms. This is the 

 usual way of expressing the dimensions of this animal, but 

 it is apt to give an exaggerated idea of its actual size. 



