II. PISCES. Characterized by having the or gans of respiration (gills) and the organs of loco motion (paired fins) adapted for an aquatic life. The class is divided into subclasses, as follows: (1) E/osmobronchii,—Pisces with a skeleton composed essentially of cartilage—the sharks, rays, etc., divided into three orders, Cladoselachea, Pleuraeant hea, Acanthodea, and Selachii. The first three are represented by Paleozoic foFisil forms. The last includes many extinct and all the existing forms.
(2) Holocephali.—Shark-like Pisces, with a large compressed head and a single external branchial aperture. It includes only the fam ily GhimTridaz (chimeras).
(3) Teleostomi.—Pisces 'distinguished from the Elasmobranehii and Holocephal i by having the primary skull and shoulder-girdle com plicated by the addition of membrane bones, and by possessing bony instead of horn-like fin rays.' This includes all of the common `bony fishes,' as well as the so-called ganoid fishes. Its orders are: Crossopterygii (bi chir, etc.) ; Chondrostei (sturgeons) ; Ho lostei (gar-pikes, etc.) ; Teleostei (bony fishes generally). The first three orders are fre quently grouped together as `Ganoidei.' (4) Dipnoi.—Pisces with lung-like respiratory organs as well as gills, and the fins con structed on the type of the archipterygium. It includes the lung-fishes, and by some au thors is made a separate class altogether. Its orders are Alonopneumona and Dipneumona.
(5) Ostracodermi (q.v.).—A group of uncer tain limits and affinities, known only from Paleozoic fossils, "characterized by the ex traordinary development of the exoskeleton (bony plates) of the head, and the absence. in all the fossil remains hitherto found, of endoskeleton, including jaws." BIBLIOGRAPHY. Bloch, A llgeniciac Nat rgeBibliography. Bloch, A llgeniciac Nat rge- schiehte der Fische (Berlin, 1782-95) ; Cuvier and Valenciennes, natvrelle des poissons (22 vols., Paris, 192S-49) ; Giinther, Catalogue of
Fishes in British M ((SCUM (Lond on. 1359-70 ) ; Oiinther, Introduction to the Study of Fishes (Edin burgh, ISSO) ; Dean, Fishes, Living and Fossil (New York, 1395). Consult also various works on the comparative anatomy of vertebrates, sueh as Huxley, Gegenbaur, Owen. Parker and Has well, Wiedersheim, etc. Of faunal works the principal are: Jordan and Evermann, Fishes of North and Middle America (4 vols., Washington, 1396-1900) ; Goode and Bean. Oceanic Ichthyology (Wasbing,ton. 18951; Goode, American Fishes (New York, 1333) : annual Reports and Bulletins of the United States Commission of Fish and Fish eries and of the National Museum (Washington, 1870 onward) ; governmental documents issued by Canada and Newfoundland; Eigenmann, South American Fishes (San Francisco, 1893) ; Var rell, History of British Fishes (3d ed., Lon don, 1859) ; Couch, History of British Fishes (London. 1865) ; Houghton, Freshwater Fishes of Great Britain (London, ]879) ; Siebold, Die Sfrsswasserhscche von Mit teleu rope (Leipzig, 2S63); Blanchard. Les poissons (Rs came dances de la France (Paris, 1866) ; Day, Fauna of Brit ish India: Fishes (London, 1889) ; Hutton and hector, Fishes of Xew Zealand (Wellington, 872). For fossil fishes, consult Woodward, Out lines of Vertebrate Paleontology (Cambridge. 1898), in which is a full bibliography to the fos sil forms; Agassiz. Recherches sur les poissons fossiles, vols. i.-iii. and supplement (Neufchatel, 1833-44) ; Woodward, Catalogue of Fossil Fishes of the British Museum, vols. i.-iii. (London, 1889 95) ; and for American forms, Newberry, "Pale ozoic Fishes of North America," in Monographs of the United States Geological Survey, vol. xvi. (Washington, 1890).