ic.

Fam. 2. _Aulacoceratidae_. Extinct; phragmacone with widely
separated septa; rostrum well developed and claviform.
_Aulacoceras_, Trias. _Atractites_, Trias and Jurassic.
_Xiphoteuthis_, Lias.

Fam. 3. _Belemnitidae_. Extinct; phragmacone short with ventral
siphuncle, prolonged dorsally into long proostracum; rostrum large
and cylindrical. _Belemnites_, 350 species from Jurassic and
Cretaceous. _Diploconus_, Upper Jurassic.

Fam. 4. _Belopteridae_. Extinct; rostrum and phragmacone well
developed, phragmacone often curved; initial chamber small.
_Beloptera_, Eocene. _Bayanoteuthis_, Eocene. _Spirulirostra_,
Miocene.

Fam. 5. _Spirulidae_. Dorsal and ventral sides of posterior
extremity of shell uncovered by mantle; no rostrum or proostracum;
shell calcareous, coiled endogastrically and sipnunculated; fins
posterior. _Spirula_, three living species known, abyssal.

Fam. 6. _Ommatostrephidae_. Shell internal and chitinous, ending
aborally in a little narrow cone; tentacular arms short and thick;
suckers with denticulate rings. _Ommatostrephes_, fins aboral,
simple and rhomboidal, British. _Ctenopteryx_, fins pectinate, as
long as the body; _Bathyteuthis_, fins terminal, rudimentary;
tentacular arms, filiform; abyssal. _Rhynchoteuthis_, tentacular
arms united to form a beak-shaped appendage. _Symplectoteuthis.
Tracheloteuthis. Doridicus. Architeuthis_; this is the largest of
Cephalopoda, reaching 60 ft. in length including arms.

Fam. 7. _Thysanoteuthidae_. Arms enlarged, bearing two rows of
suckers and filaments; fins triangular, extending whole length of
body. _Thysanoteuthis_, Mediterranean.

Fam. 8. _Onychoteuthidae_. Fins terminal; tentacular arms long;
suckers with hooks. _Onychoteuthis_, hook-bearing suckers on
tentacular arms only. _Enoploteuthis_, hook-bearing suckers on all
the arms. _Veranya_, body very short, tentacular arms atrophied in
the adult, Mediterranean. _Chaunoteuthis_, body elongated,
tentacular arms atrophied. _Pterygioteuthis. Ancistroteuthis.
Abralia. Teleoteuthis. Lepidoteuthis._

Fam. 9. _Gonatidae_. Body elongated; fins terminal; radula with only
two lateral teeth. _Gonatus_.

Fam. 10. _Cheiroteuthidae_. Tentacular arms long, not retractile;
resisting apparatus well developed. _Cheiroteuthis_, suckers along
the whole leng