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.  Beloteuthis, Miinster, 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. 
Fic. 300. 
Opisthoteuthis depressa, Ijima and Ikeda, dorsal aspect. «7, arms; e, eye; fi, fin; fu, funnel. 
(After Ijima and Ikeda.) 
SuB-ORDER 2. OcToOPoDaA. 
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 CrRRHOTEUTHIDAE, Keferstein. Arms united by a mem- 
brane, and bearing tentacular filaments on either side of the suckers 
(Fig. 260). Genera—Ctrrhoteuthis, Eschricht ; the pallial sac prominent 
and the fins large; a pelagic form.  Opzisthoteuthis, 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. 
