SUBORDER I  . DECAPODA.—FOUr pairs of

ordinary non-retractile arms which are shorter than the body, and one pair of tentacular arms, situated between the third and fourth normal arms on each side and retractile within special pouches . Suckers pedunculated and provided with horny rings, on the tentacular arms confined usually to the distal extremities . Usually a well-developed internal shell, and lateral fins on the edges of the body . Heart in a coelomic cavity; nidamentary glands usually present . Tribe i . Oigopsida.—A wide aperture in the cornea . Two oviducts in the female . In fossil genera and Spirula, shell has a multi-!ocular phragmacone with a siphuncle; initial chamber globular and larger than the second chamber . The most ancient forms characterized by the small size of the rostrum and proostracum, and large a (After Lankester.) ing as an invagination of the outer cell-layer . Mantle-skirt . Gill .

Pen-sac or shell-sac, now closed . Dorsal groove . Primitive optic vesicle, now closed (see fig . 34) . Lens . Retina . Second or anterior optic chamber still open . Iridean folds . The primitive invagination to form one of the otocysts, as seen in fig . 35 (5) and (6) . size of the phragmacone . In the living genera, except Spirula, the shell is a chitinous gladius .

Fam . I . Belemnoteuthidae .

Extinct; shell with well-developed phragmacone, and rostrum merely a calcareous envelope; siphuncular necks directed backwards as in Nautiloidea; ten equal arms provided with hooks . Phragmoteuthis, Trias . Belemnoteuthis, Jurassic and Cretaceous . Acanthoteuthis, Jurassic . 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 siphunculated; 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 appenda>e . Symplectoteuthis . Tracheloteuthis . Doridicus . Architeuthis; tiis is the largest of Cephalopoda, reaching 6o 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. to . Cheiroteuthidae . Tentacular arms long, not retractile; resisting apparatus well developed . Cheiroteuthis, suckers along the whole length of the tentacular arms . Doratopsis, body very long and slender with aboral spine, dorsal arms very short . Histioteuthis, six dorsal arms united by membrane, photogenous organs present .

Histiopsis, membrane of dorsal A, Pinnocto pus cordiformis, Quoy and Gain (from New

Zealand) . B, Tremocto pus violaceus, Ver . (from the Mediterranean) . C, Cranchia scabra, Owen (from the Atlantic Ocean; one of the Decapoda) . D, Cirrhoteuthis Mulleri, Esch . (from the Greenland coast). arms only half-way up the arms, photogenous organs present . Calliteuthis, no brachial membrane, photogenous organs present . Grimalditeuthis, two fins on each side, no tentacular arms . Fam. ii . Cranchiidae . Eight normal arms, very short; eyes prominent; fins small and terminal . Cranchia, body short, purse-shaped, normal arms short, fins entirely aboral .

Loligopsis, body elongated, conical, tentacular arms slender . Leachia, tentacular arms absent,

funnel without a valve . Taonius, body elongated, normal arms, rather short, eyes pedunculated . Tribe 2 . Myopsida.—No aperture in the cornea . Left oviduct only developed in female . Internal shell without a distinct phrag- macone, calcified or simply chitinous . Fam. t . Sepiidae . Body wide and flat; fins narrow, extending the whole length of the body; shell calcareous and laminated . Belosepia, a rudiment of rostrum and phragmacone present in shell, Eocene . Sepia, shell with a rostrum, British .

Sepiella, shell without a rostrum . Same

stage as fig . 35 (4) . Same stage as fig . 35 (8) ; only the left side of the sections is drawn, and the food-material which occupies the space internal to the membrane ym is omitted . Rectum . Ink-sac . Outer cell-layer . Middle cell-layer . Deep cell-layer of fusiform cells (yolk-membrane) . Optic nerve-ganglion . Otocyst .

The "

white body " of the adult ocular capsule form- A, B, al, is, ep, mes, ym, ng, ot, wb, mtf, g, Ps, dg, Poe . 1, r, soc, 702 Fam . 2 . Sepiolidae . Body short, rounded at the aboral end; fins rounded, inserted in middle of body-length; shell chitinous, small or absent . Sepiola, head united to mantle dorsally, British . Rossia, head not united to mantle, British . Stoloteuthis and Inioteuthis, without shell . Heteroteuthis . Euprymna . Fam . 3 .

Idiosepiidae . Body elongated, with rudimentary terminal fins; internal shell almost lost . Idiosepius, 1.5 cm. long,

Indian Ocean . Fam . 4 . Sepiadariidae . Body short; mantle united to head dorsally; no shell . Sepiadarium, Pacific Ocean . Sepioloidea, Australian . Fam . 5 . Loliginidae .

Body elongated and conical; fins extending forward beyond the middle of body-length; shell chitinous, well developed . Loligo, fins 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; Phylloleuthis, Cretaceous; Plesioteuthis, Jurassic and Cretaceous .