SUBPHYLUM D. VERTEBRATA. DIVISION (I). CYCLOSTOMATA. Order 1. MARSIPOBRANCHII. Family =Myxinoidei=. Myxine--hag-fish. Bdellostoma. Family =Petromyzontidae=. Petromyzon--lamprey. (Ammocoetes--larval lamprey.) Family =Palaeospondylidae=. _Palaeospondylus._ Order 2. OSTRACODERMI. Suborder 1. HETEROSTRACI. Family =Pteraspidae=. _Pteraspis._ Suborder 2. OSTEOSTRACI. Family =Cephalaspidae=. _Cephalaspis._ Suborder 3. ANTIARCHA. Family =Asterolepidae=. _Pterichthys._ _Asterolepis._ DIVISION (II). GNATHOSTOMATA. A. ICHTHYOPSIDA. CLASS I. PISCES. Order 1. ELASMOBRANCHII. Suborder (1). ICHTHYOTOMI. Family =Pleuracanthidae=. _Xenacanthus._ Suborder (2). PLEUROPTERYGII. _Cladoselache._ Suborder (3). SELACHII. Group SQUALIDAE. Family =Notidanidae=. Heptanchus. Hexanchus. Chlamydoselache--frill-gilled shark. Family =Cochliodontidae=. _Cochliodus._ Family =Cestraciontidae=. Cestracion--Port Jackson shark. _Acrodus._ Family =Scylliidae=. Scyllium--spotted dogfish. Family =Lamnidae=. Odontaspis. Family =Carcharidae=. Galeus--tope. Family =Spinacidae=. Acanthias--spiny dogfish. Scymnus. Family =Squatinidae=. Squatina (Rhina)--angel fish. Group BATOIDEI. Family =Pristidae=. Pristis--saw-fish. Family =Raiidae=. Raia--skate. Family =Myliobatidae=. Myliobatis--eagle ray. Family =Trygonidae=. Trygon--sting ray. Family =Torpedinidae=. Torpedo--electric ray. Suborder (4). ACANTHODII. Family =Acanthodidae=. _Acanthodes._ Family =Diplacanthidae=. _Diplacanthus._ Order 2. HOLOCEPHALI. Family =Chimaeridae=. Chimaera--rabbit fish. Harriotta. Callorhynchus. _Ischyodus._ Order 3. GANOIDEI. Suborder (1). CHONDROSTEI. Family =Palaeoniscidae=. _Palaeoniscus._ _Trissolepis._ Family =Acipenseridae=. Acipenser--sturgeon. Scaphirhynchus. Family =Polyodontidae=. Polyodon (Spatularia)--spoon-beaked sturgeon. Psephurus--slender-beaked sturgeon. Suborder (2). CROSSOPTERYGII. Family =Holoptychiidae=. _Holoptychius._ Family =Rhizodontidae=. _Rhizodus._ Family =Osteolepidae=. _Osteolepis._ Family =Polypteridae=. Polypterus--bichir. Calamoichthys--reed-fish. Suborder (3). HOLOSTEI. Family =Lepidosteidae=. Lepidosteus--gar pike. Family =Semionotidae=. _Lepidotus._