342 THE CEPHALOPODA 



rounded, and extending farther forward than the aboral half of the body. 

 Tentacular arms partly retractile. The shell is a well-developed chitinous 

 gladius (Fig. 263). Genera Loligo, Lamarck ; fins triangular, confined 

 to the aboral half of the body ; British. Sepioteuthis, de Blainville ; fins 

 prominent but rounded, extending over the whole length of the body. 

 Loliolus, Steenstrup. Loliguncula, Steenstrup. The following fossil 

 genera, known by their gladius and ink -sac, have been placed near 

 Loligo : Teuthopsis, Deslongchamps. Seloteuthis, Munster, and Geoteuthis, 

 from the Lias, and Phylloteuthis, Meek and Hayden, from the Cretaceous, 

 are distinguished by their broader gladius. Plesioteuthis, Wagner, from 

 the Jurassic and Cretaceous, has a long and narrow gladius. 



FIG. 300. 



Opifthoteuthis dtpressa, Ijiina and Ikeda, dorsal aspect, ur, arms ; e, eye ; fi, fin ; /, funnel. 

 (After Ijima and Ikeda.) 



SUB-ORDER 2. OCTOPODA. 



These Dibranchia have only eight arms, which are all similar and 

 are longer than the body. The body is short and rounded aborally. 

 The suckers are sessile. The heart is not contained in the coelom. 

 There are no nidamentary glands. The Octopoda comprise two tribes, 

 the Leioglossa and Trachyglossa. 



TRIBE 1. LEIOGLOSSA. 



The members of this tribe have no radula. All the arms are united 

 together by a complete membrane. Fins are developed on the sides of 

 the body. 



Family CIRRHOTEUTHIDAE, Keferetein. Arms united by a mem- 

 brane, and bearing tentacular filaments on either side of the suckers 

 (Fig. 260). Genera Cirrhoteuthis, Eschriclit ; the pallial sac prominent 

 and the fins large ; a pelagic form. Opisthoteuthis, Verrill ; body 

 flattened, with small fins ; a deep-sea form (Fig. 300). Vampyroteuthis, 

 Chun ; four fins. Some fossil Octopoda bearing fins are known ; e.g. 

 Palaeoctopus, Woodward, from the Cretaceous. 



