THE FISHES OF THE DEEP SEA 296 Deep-sea fishes a recent discovery, 296--Physical conditions affecting these fishes, 297--Characteristics of Deep-sea fishes, 299--Their vertical and horizontal distribution, 304--List of Deep-sea fishes, 305. SYSTEMATIC AND DESCRIPTIVE PART. FIRST SUB-CLASS--PALÆICHTHYES. PAGE FIRST ORDER--CHONDROPTERYGII 313 I. _Plagiostomata_ 313 A. _Selachoidei--Sharks_ 314 Families: Carchariidæ (Blue Shark, Tope, Hammerhead, Hound), 316--Lamnidæ (Porbeagle, Carcharodon, Fox-Shark, Basking-Shark), 319--Rhinodontidæ, 323--Notidanidæ, 324--Scylliidæ (Dog-fishes), 325--Hybodontidæ, 328--Cestraciontidæ (Port Jackson Shark), 328--Spinacidæ (Spiny Dogs, Greenland Shark), 330--Rhinidæ, 334--Pristiophoridæ, 335. B. _Batoidei--Rays_ 335 Families: Pristidæ (Saw-fishes), 336--Rhinobatidæ, 337--Torpedinidæ (Electric Rays), 338--Rajidæ (Rays and Skates), 340--Trygonidæ (Sting Rays), 342--Myliobatidæ (Eagle Rays), 344. II. _Holocephala_ 348 Family: Chimæridæ, 348. SECOND ORDER--GANOIDEI 350 I. _Placodermi_ 351 II. _Acanthodini_ 355 III. _Dipnoi_ 355 Families: Sirenidæ (Lepidosiren, Protopterus, Ceratodus), 355--Ctenododipteridæ, 359--Phaneropleuridæ, 360. IV. _Chondrostei_ 360 Families: Acipenseridæ (Sturgeons), 360--Polyodontidæ, 362. V. _Polypteroidei_ 363 Families: Polypteridæ, 364--Saurodipteridæ, 365--Coelacanthidæ, 365--Holoptychidæ, 365. VI. _Pycnodontoidei_ 366 Families: Pleurolepidæ, 366--Pycnodontidæ, 366. VII. _Lepidosteoidei_ 367 Families: Lepidosteidæ, 367--Sauridæ, 368--Stylodontidæ, 368--Sphærodontidæ, 368--Aspidorhynchidæ, 369--Palæoniscidæ, 369--Platysomidæ, 370. VIII. _Amioidei_ 370 Families: Caturidæ, 371--Leptolepidæ, 371--Amiidæ (Bow-fin), 371. SECOND SUB-CLASS--TELEOSTEI. FIRST ORDER--ACANTHOPTERYGII 374