mollusca: cephalopoda. 



329 



;::^^ii 



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 

 ultimately beconxes " hectocotylised." 



Section B. Decapoda. — The Ce- 

 phalopods of this section have eight 

 arms and two additional " tentacles," 

 which are much longer than the true 

 arras, are retractile, and have expand- 

 ed club'Shaped extremities (fig. 115). 

 The suckers are pedunculated; the 

 body is always provided with lateral 

 fins, and the shell is always internal. 



This section comprises the three 

 " living families of the Teuthida, S(J>i- 

 adce, and the Spirulidce, and the extinct 

 family of the Bekmnitida. 



The family of the Teuthidce com- 

 prises the Calamaries or Squids, cha- 

 racterised by the possession of an 

 elongated body with lateral fins. 

 The shell is internal and horny, con- 

 sisting of a median shaft and of two 

 lateral wings ; it is termed the " gladi- 

 us " or " pen," and in old specimens 

 several may be found lodged in the 

 mantle, one behind the other. In 

 the common Calamary (Loligo) the 

 fourth left arm of the male is meta- 

 morphosed towards its extremity to 

 subserve reproduction. 



In the family of the Sepiadce the 

 internal shell is calcareous ("cuttle- 

 bone" or " sepiostaire "), and is in 

 the form of a broad plate, having an 

 imperfectly chambered apex. The 

 broad laminated plate is extremely 

 light and spongy, and the chambered 

 apex is called the " mucro." In the 

 living members of the family the body 

 is pirovided with long lateral fins, sometimes as long and as wide 

 as the body itself. 



In the singular family of the Spirulida the internal skeleton is 

 in the form of a nacreous, discoidal shell, the whorls of which 



Fig. 118. — Diagram of Belem- 

 nite (after Frpfessor Phillips). 

 r Horny pen or "pro-ostra- 

 cum ; ", jt Chambered "phrag- 

 macone'* in its cavity (t?) or 

 •* alveolus \" g " Guard. 



