MOLLUSCA: CEPHALOPODA. 429 



Teuthida, Sepiadce, and the Spiriilida, and the extinct family 

 of the Beltmnitida. 



The family of the Teuthidcz comprises the Calamaries or 

 Squids (fig. 231), characterised by the possession of an elon- 

 gated body with lateral fins. The shell (fig. 229, b) is internal 

 and horny, consisting of a median shaft and of two lateral 

 wings; it is termed the "gladius" or "pen," and in old speci- 

 mens 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 metamorphosed towards its extremity to 

 subserve reproduction. 



In the family of the Sepiadce the internal shell (fig. 229, a) 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 provided with long lateral 

 fins, sometimes as long and as wide as the body itself. 



In the singular family of the Spirulida the internal skeleton 

 (fig. 229, c) is in the form of a nacreous, discoidal shell, the 

 whorls of which are not in contact with one another, and which 

 is divided into a series of chambers by means of partitions or 

 septa which are pierced by a ventral tube or "siphuncle." 

 The body is provided with minute lateral fins, and the arms 

 have six rows of small suckers. The shell of the Spirula 

 commonly known as the " post-horn " is similar in structure 

 to the shell of the Nautilus, but it is lodged in the posterior 

 part of the body of the animal (fig. 229), and is therefore inter- 

 nal, whereas the shell of the latter is external It really corre- 

 sponds to the " phragmacone " of the Belemnite. Though the 

 shell occurs in enormous numbers in certain localities, a single 

 perfect specimen of the animal is all that has been hitherto 

 obtained. In its internal anatomy, Spirula is a true Dibran- 

 chiate. It has the peculiar feature that the hinder end of the 

 body forms a kind of suctorial disc, apparently employed to 

 moor the animal to foreign bodies. The beaks are not calci- 

 fied. The retractor muscles of the funnel spring from the inner 

 surface of the last chamber of the shell (as in Nautilus} ; and 

 this chamber also lodges the hinder termination of the liver 

 (Owen). 



In the extinct family of the Belemnitida, our knowledge is 

 chiefly confined to the hard parts. Certain specimens how- 

 ever, have been discovered, which show that the Belemnite had 

 essentially the structure of a Cuttle-fish, such as the recent 

 Calamary. The body was provided with lateral fins ; the arms 



