276 MANUAL OF ZOOLOGY. 



similar to one another, and united at the base by a web. There 

 is an internal rudimentary shell, represented by two short 



Pig. 84. Argonauta argo, the 4 Paper Nautilus,' female. The animal is repre- 

 sented in its shell, but the webbed dorsal arms are separated from the shell, 

 which they ordinarily embrace. 



styles encysted in the substance of the mantle. (Owen.) 

 The body is seldom provided with lateral fins. The third 

 right arm of the male is primarily developed in a cyst, and 

 iiltimately becomes ' hectocotylised.' 



SECTION B. DECAPODA. The Cephalopods of this section have 

 eight arms and two additional 'tentacles,' which are much 

 longer than the true arms, and have expanded club-shaped 

 extremities. The suckers are pedunculated ; the body is 

 always provided with lateral fins, and the shell is always in- 

 ternal (jig. 82). 



This section comprises the three living families of the 

 Teuthidce, Sepiadce, and the SpiruLidae, and the extinct family 

 of the Belemnitidce. 



The family of the Teutliidm comprises the Calamaries or 

 Squids, characterised by the possession of an elongated body, 

 with lateral fins. The shell is internal and horny, consisting 

 of a median shaft and of two lateral wings ; it is termed the 

 ' gladius' or ' pen,' and in old specimens several may be found 

 lodged in the mantle, one behind the other. In the common 



