DECAPODA 389 



four rows, fourth left arm in the male hectocotylised near the 

 base (Fig. 240). — World-wide. 



The sepion or ' cuttle-bone ' runs the whole length and width 

 of the body. In Sepia it is very thick in front, while the 

 posterior ventral end is concave and terminated ])y a prominent 

 spine, the rostrum or mucro, which points downwards. The 

 whole shell is surrounded by a thin 

 chitinous margin, which forms a 

 lateral expansion. Other genera are 

 tSepiella, Hemisepius, and Trachyteu- 

 ^/m (fossil only). '''-^\l^^ :-V'%0y 



C. Chondrophora. — ^\\(i\l{gladius \ -"^j'^^l^Cp 



or p)en) long, chitinous. "" ^ £m 



(a) Myopsidae : ^ cornea entire, ^ ... „ . ,' ... ,, , 

 \ ^ " -^ . Fig. 249. — Hectocotylised arm (/;.«) 



species mostly sub-littoral. of Se2n.a officinalis L., shown in 



' Fam. 1. Sepiolidae.—Yins large, ''°"^f '*^ ^° °"^ °'' ^^'^ ""I'^'''^''^ 



■'- ' sessile arms ; in, mouth ; %>, 



dorso-lateral ; tentacular arms retrac- pocket into which the tentacular 



tile; two first dorsal arms in the ••^•■>" i« retracted. 



male hectocotylised ; gladius narrow, half as long as the body. — 



AVorld-wide. 



Frincipal genera : Scpiola, dorsal mantle connected with the 

 head by a broad cervical band, ventral mantle with the funnel l)y 

 a ridge fitting into a groove ; Rossia, dorsal mantle supported 

 by a ridge, arms witli never more than four rows of acetabula ; 

 Inioteuthis, Stoloteuthis, Nectoteuthis, and Fromachotcuthis. 



Fam. 2. Sepiadariidae. — Fins not as long as the body, mantle 

 united to the head on the dorsal side, fourth left arm in the 

 male hectocotylised ; no gladius. Principal genera, Sepiadarium, 

 Sepioloidea. — Chiefly Pacific Ocean. 



Fam. 3. Idiosepiidae. — Fins very small, terminal ; fourth 

 pair of arms in the male hectocotylised, bare of suckers. 



The only genus, Idioscpion, with a single species (/. 2^yg- 

 macmn Stp.) is from the Indian ocean, and is the smallest 

 known Cephalopod, measuring only about 15 mm. in length. 



Fam. 4. Loliginidac — Body rather long, fins varying in size, 

 tentacular arms partially retractile, gladius as long as the back, 

 pointed in front, shaft keeled on the ventral side.— World-wide. 



LoUcjo proper has a pointed body with triangular posterior 

 fins united behind; sessile arms with two rows of acetabula, 

 ' txviiji, close the eyes ; cSi/i?, sight ; (.'ontrasted witli Oigo2)sidac (otyw, open). 



