s triangular, aboral, British.
_Sepioteuthis_, fins rounded, extending along whole of body-length.
_Loliolus. Loliguncula._ The following fossil genera, known only by
their gladius and ink-sac, have been placed near
_Loligo_:--_Teuthopsis, Beloteuthis_ and _Geoteuthis_, Lias;
_Phylloteuthis_, Cretaceous; _Plesioteuthis_, Jurassic and
Cretaceous.

SUBORDER 2. OCTOPODA.--Only four pairs of arms, all similar and longer
than the body. Body short and rounded aborally. Suckers sessile. Heart
not contained in coelom. No nidamentary glands.

[Illustration: FIG. 39.--_Palaeoctopus Newboldi_, the oldest Octopod
known. From the Cretaceous rocks of Lebanon. (After H. Woodward.)]

Tribe I. _Leioglossa_.--No radula. Arms united by a complete membrane.
Fins on sides of body.

Fam. _Cirrhoteuthidae_. Tentacular filaments on either side of the
suckers. _Cirrhoteuthis_, pallial sac prominent, fins large,
pelagic. _Opisthoteuthis_, body flattened, with small fins,
deep-sea. _Vampyroteuthis_, four fins. _Palaeoctopus_, fossil,
Cretaceous.

Tribe 2. _Trachyglossa._--Radula present. No fins.

Fam. 1. _Amphitretidae_. Arms united by membrane; funnel attached to
mantle, dividing the pallial aperture into two. _Amphitretus_,
pelagic.

Fam. 2. _Alloposidae_. All arms united by membrane; mantle joined
to head by dorsal band and two lateral commissures. _Alloposus_,
pelagic.

Fam. 3. _Octopodidae_. Arms long and equal, without membrane;
hectocotylus not autotomous. No cephalic aquiferous pores.
_Octopus_, two rows of suckers on each arm, British. _Eledone_,
single row of suckers on each arm. _Scaeurgus. Pinnoctopus.
Cistopus. Japetella._

Fam. 4. _Philonexidae_. Hectocotylus autotomous; arms unequal in
size; aquiferous pores on head and funnel. _Tremoctopus_, two dorsal
pairs of arms united by membrane. _Ocythoe_, without interbrachial
membrane.

Fam. 5. _Argonautidae_. Hectocotylus autotomous; no interbrachial
membrane; extremities of dorsal arms in female expanded and
secreting a shell; males very small, without shell. _Argonauta_.

LITERATURE.--Use has been freely made above of the article by E. Ray
Lankester, on _Mollusca_, in the 9th edition of this Encyclopedia. For
the chief modern works, see Bashford Dean, "Notes on Living Nautilus,"
_Amer. Nat._ xxxv., 1901; Arthur Willey, "Contribution