SORTH-CABOLINA GEOLOGICAL SURVEY, 



24:5 



CHAPTER XVIII. 







MOLLUSCA. CLASS CEPHALOPODA. 



Tills class embraces those mollusca, whose locomotive or- 

 gans are attached to the head. They have the form of mus- 

 cular arms or tentacles. Besides the arms surrounding the 

 head, they have fins and an apparatus by which they can pro- 

 pel themselves through the water by its ejection in a stream. 



Some are covered by a shell, coiled in a vertical plane, 'as 

 the nautilus ; others are naked or destitute of an external 

 shell, but have an internal one, which varies much in form in 

 the different families. 



Their eyes are well developed and their mouths are provi- 

 ded with jaws somewhat similar to the mandibles of a bird. 

 They are predatory and live on fish, crabs and shell fish. 



The most remarkable part of the apparatus by which they 

 seize their prey, are the circular discs arranged on the under 

 side of their arms, by which they are enabled to produce in- 

 stantaneously a vacuum when applied to the surface of a fish 

 or a slightly yielding body. By this arrangement they are 

 able to seize and hold most securely their captives, and de- 

 vour them at leisure. As a means of escape from enemies 

 more powerful than themselves, they are provided with a bag 

 or sac filled with a dark fluid which they can eject at will, and 

 thereby discolor the surrounding water and escape unseen. 



This sac is called the ink-bag, and the liquid is employed 

 for the manufacture of the India ink. Even the consolidated 

 fluid in the fossil ink-bags is used for this purpose. 



This class is a large one, and the species which compose it 

 are found in all seas. They were also extremely numerous 

 in ancient times, and their hard parts as external and internal 

 shells are preserved as relics of extinct races. One of the 

 most common fossils of the green sand is the Belemnite,* 

 which is an internal shell, though its form is quite unlike one. 



* From belemnon, a dart. 



