CLASSIFICATION.] ICHTHYOLOGY 087 that it is provided with a lung. It is much more probable, how ever, that it rises now and then to the surface of the water in order to fill its lung with air, and descends again until the air is so much deoxygenized as to render a renewal of it necessary. As the barramunda has perfectly developed gills, as well as the lung, we can hardly doubt that, when it is in water of normal composi tion, and "pure enough to yield the necessary supply of oxygen, these organs are sufficient for the purpose of breathing, and that the respiratory function rests with them alone. But when the fish is compelled to sojourn in thick muddy water charged with gases which are the products of decomposing organic matter (and this must very frequently be the case during the droughts which annu ally exhaust the creeks of tropical Australia), it commences to breathe air with its lung in the way indicated above. If the medium in which it happens to be is altogether unfit for breathing, the gills cease to have any function ; if it is irrespirable in a less degree the gills may still continue to assist the lung. The barra munda, in fact, can breathe by either gills or lung alone, or by both simultaneously. The discovery of Ceratodus does not date farther back than the year 1870. It proved to be of the greatest interest, not only on account of the relation of this creature to the other living Dipnoi and Oanoidei, but also because it threw fresh light on those singu lar fossil teeth which are found in strata of the Triassic and Jurassic formations in various parts of Europe, India, and America. These teeth vary greatly in general shape and size ; they are sometimes 2 inches long, much longer than broad, depressed, with a flat or slightly undulated always punctuated crown, with one margin con vex, and with from three to seven prongs projecting on the opposite margin. Family 2. Ctenododipteridce. Caudal fin heterocercal ; gular plates ; scales cycloid. Two pairs of molars and one pair of vome- rine teeth. Extinct. Dipterus (Ctenodus), Heliodus, from Devonian strata. Family 3. Phaneroplcuridce. Caudal fin diphy cereal; vertical fin continuous ; gular plates ; scales cycloid. Jaws with a series of minute conical teeth on the margin. Extinct. Phan&ropleuron, from Devonian and Carboniferous for mations. SUBORDER IV. Chondrostd. Skeleton notochordal; skull cartila ginous, with dermal ossifications ; branchiostegals few in number or absent. Teeth minute or absent. Integuments naked or with bucklers. Caudal fin heterocercal, with fulcra. Nostrils double, in front of the eyes. Family 1. Acipenseridce. Body elongate, sub-cylindrical, with five rows of osseous bucklers. Snout produced, subspatulate or conical, with the mouth at its lower surface, small, transverse, pro tractile, toothless. Four barbels in a transverse series on the lower side of the snout. Vertical fins with a single series of fulcra in front. Dorsal and anal tins approximate to the caudal. Branchio- stegals none. Air-bladder large, simple, communicating with the dorsal wall of the oesophagus. Genera : Acipenscr and Scaphirhynclius (Sturgeons, Hausen, Sterlet). Family 2. Polyodontidce. Body naked, or with minute stellate ossifications. Mouth lateral, very wide, with minute teeth in both jaws. Barbels none. Caudal fin with fulcra. Dorsal and anal fins approximate to the caudal. Genera: Polyodon and Pscphurus. Fossil: Chondrosteus. SUBORDER V. Polypteroidei. Paired fins with axial skeleton, fringed ; dorsal fins two or more. Branchiostegals absent, but generally gular plates. Vertebral column diphycercal or heterocer cal. Body scaly. Family 1. Polypteridce, Scales ganoid ; fins without fulcra. A series of dorsal spines, to each of which an articulated finlet is attached ; anal placed close to the caudal fin, the vent being near the end of the tail. Abdominal portion of the vertebral column much longer than the caudal. Genera : Polypterus and Calamoichihys. Polyptcrus is confined to tropical Africa, occurring in abundance in the rivers of the west coast and in the upper Nile; it is rare in the middle and lower Nile. There is only one species known, Polypterus bichir (" Bichir " being its vernacular name in Egypt), which varies in the number of the dorsal linlets, the lowest being eight, the highest eighteen. It attains to a length of 4 feet. Nothing is known of its mode of life, observations on which are very desirable. Calamoichthys (from Old Calabar) is distinguished from Polypterus by its greatly elon gated form and the absence of ventral fins. Family 2. Saurodipteridce. Scales ganoid, smooth like the sur face of the skull. Two dorsal fins ; paired fins obtusely lobate. Teeth conical. Caudal fin heterocercal. Extinct. Diplopterua, Mcgalichthys, and Ostcolc2n-s, from Devon ian and Carboniferous formations. Family 3. Guelacanthuicc. Scales cycloid. Two dorsal fins, each supported by a single two-pronged interspinous bone ; paired tins obtusely lobate. Air-bladder ossified ; iiotoohord persistent, diphycercal. Extinct. Ccelacanthus, from Carboniferous strata. Several other genera, from the Coal formations to the Chalk, have been associated with it: Undina, Graphiurus, Macropoma, Holophayus, Hoplo- pygus, llhizodus. Family 4. Holoj>tychidac. Scales cycloid or ganoid, sculptured. Two dorsal fins ; pectorals narrow, acutely lobate ; dentition deii- drodont. Extinct. Genera : Iloloptychius, Saurichthys, Gfyptolepw, Dcn- drodus, Gly]itolccmus, (Jlyptopoinus, Tristichopterus, Qyroptychiua, Strepsodus, from Devonian ..aid Carboniferous strata. .SUBORDER VI. Pycnodontoidei. Body compressed, high and short or oval, covered with rhombic scales arranged in decussating pleuro- lepidal lines. Notochord persistent. Paired fins without axial skeleton. Teeth on the palate and hinder part of the lower jaw molar-like. Brauchiostegals, but no gular plates. Extinct. Family 1. Pleurolepidce. Homocercal. Body less high. Fins with fulcra. Genera: Plcurolepis and Homceolepis, from the Lias. Family 2. Pi/cnodontidcc. Homocercal. The neural arches and ribs are ossified ; the roots of the ribs are but little expanded in the older genera, but are enlarged in the Tertiary forms, so as to simulate vertebra?. Paired fins not lobate. Obtuse teeth on the palate and the sides of the mandible ; maxilla toothless ; incisor-like teeth in the intermaxillary and front of the mandible. Fulcra absent in all the fins. Genera : Gyrodus, Mcsturus, Microdon, Cwlodus, Pycnodus, Mcsodon, from Mesozoic and Tertiary formations. SUBORDER VII. Lcpidostcoidci. Scales ganoid, rhombic; fins generally with fulcra ; paired fins not lobate. Pneoperculum and interoperculum developed ; generally numerous branchio stegals, but no gular plate. Family 1. Lepidosteidce. Scales ganoid, lozenge-shaped. Skele ton completely ossified ; vertebrae convex in front and concave be hind. Fins with fulcra ; dorsal and anal composed of articulated rays only, placed far backwards, close to the caudal. Abdominal part of the vertebral column much longer than caudal. Branchio stegals not numerous, without enamelled surface. Heterocercal. Lepidosteus. This genus existed as early as Tertiary times; their remains have been found in Europe as well as in North America. In our period they are limited to the temperate parts of North America, Central America, and Cuba. Three species can be distinguished, which attain to a length of about 6 feet. They feed on other fishes ; and their general resemblance to a pike has gained for them the vernacular names of "Gar-Pike" or " Bony Pike." Family 2. Sauridcc. Body oblong, with ganoid scales ; verte- brte not completely ossified ; termination of the vertebral column homocercal ; fins generally with fulcra. Maxillary composed of a
- single piece ; jaws with a single series of conical pointed teeth.
| Branchiostegals numerous, enamelled, the anterior forming broad j gular plates. Extinct. Genera : Scmionotus, Eugnathus, Cephcnoplosus, Ma- crosemius, Proptents, Ophiopsis, Pholidj)horus, Pleuropholis, Pachyeormus, Ptycholcpis, Conodus, Eulcpidotus, Lophiostomus, &c. Family 3. Sty lodont idee. Body rhombic or ovate, with ganoid scales ; vertebra? not completely ossified ; termination of the verte bral column homocercal ; fins with fulcra. Maxillary composed of a single piece ; jaws with several series of teeth, the outer ones equal, styliform. Dorsal fin very long, extending to the caudal. Branchiostegals numerous. Extinct. Tctrayonolcpis, from the Lias. Family 4. Sphcerodontidcc. Body oblong, with rhombic ganoid scales ; vertebra; ossified, but not completely closed ; homocercal ; fins with fulcra. Maxillary composed of a single piece ; teeth in several series, obtuse ; those on the palate globular. Dorsal and anal fins short. Branchiostegals. Extinct. The type genus of this family is Lepidotus. Family 5. Aspidorlnjnchida . Body elongate, with ganoid scales ; jaws prolonged into a beak ; termination of the vertebral column homocercal. Fins with fulcra ; a series of enlarged scales along the side of the body. Dorsal fin opposite to the anal. Extinct : Mesozoic. Genera : Aspidorhynchus and Belonostomits. Family 6. Palcconiscidce. Body fusiform, with rhombic ganoid scales. Notochord persistent, with the vertebral arches ossified. Heterocercal. All the fins with fulcra ; dorsal short. Branchio stegals numerous, the foremost pair forming broad gulars. Teeth small, conical, or cylindrical. Extinct. Genera : from the Old Red Sandstone Chirolcpis and Acrolepis ; from Carboniferous rocks Cosmoptyehius, Elonichthys, Nematoptychius , Cydoptychiits, Microcouodus, Gonatodits, Rhadin- ichthys, Myriolepis, Urostlienes ; from the Permian lihabdulepis, PulcBoniscus, Amblyptcrus, and Pyyojttcriw ; from the Lias Centrolcpis, Oxygnathus, Cosmoleis, and Thrissonotus. Family 7. Platysomidcc. Body generally high, compressed, covered with rhombic ganoid scales arranged in dorso- ventral bands. Notochord persistent, with the vertebral arches ossified. Hetero
cercal ; fins with fulcra ; dorsal fin long, occupying the posterior
