TABLE SHOWING THE CLASSIFICATION OF THE CEPHALOPODS 

 DESCRIBED IN THIS CHAPTER 



CLASS CEPHALOPODA 



Subclasses 

 Tetrabranchiata 



'Wibranchiata 



Orders 



fOCTOPODA 



V 



DECAPODA 



Genera 

 Nautilus 

 ( Octopus 

 \ Argonauta 

 ( Spirula 

 \ Ommastrephes 

 \ Sepia 

 f Loligo 



Species 



A. argo 



O. illecebrosus 

 L. Pealfi 

 L. brevis 



CLASS CEPHALOPODA 



The Cephalopoda form a singularly isolated group, and are so 

 superior in organization and intelligence to all other mollusks 

 that it is difficult to believe that they are first cousins to the 

 lethargic gasteropod and the simply constructed bivalve. But 

 the class bears the stamp of its origin in a mantle, a radula, and 

 a disposition of internal organs and functions which, although 

 highly perfected, is essentially molluscan. 



Along the Atlantic coast of the United States, particularly in 

 its northern portion, occur several examples of cephalopods be- 

 longing to the genera Ommastrephes and Loligo, all the species of 

 which are referred to, in common parlance, as " squids." They 

 frequent shallow water, and are often to be found in weirs, dart- 

 ing about with rapid, spasmodic movements, or perhaps lying 

 motionless on the bottom. The squids enter the weirs for the 

 purpose of capturing the young mackerel which are caught in 

 these traps. The squid lies quietly upon the bottom, which it 

 simulates so closely in color as to be almost invisible, and when 



464 



