Subclass 2. UolocephaU. CurtiUiginous fishes with four pairs o' jjill-slits, nearly coiicealcd by a »old of skin (Chima?ras) .
Subclass 3. Teleostomi. Fishes with the skeleton complicated by mem- brane-bones and ossifications, or completely bony (Sturgeons and ordinary Fish).
Subclass 4. Dipnoi. Fish-like animals, having an apparatus for breath- ing atmospheiic air ( Lung- fishes).
Subclass 5. Ostracodermi. Paleozoic fish- es, with au exoskeleton extraor- dinarily developed about the head, and ai)])arently with no endoskeleton (Cephalaspis, etc.). Class 3. Amphibia. Amphibious verte- brates, breathing ]>y gills in the larval condition, and (usually) by lungs when adult, and having legs and five-toed feet (Amphib- ians ) .
Class 4. Reptilia. Elongated, air-breathing vertebrates, with a horny epi- dermal skeleton of scales and one occipital condyle (Reptiles).
Class 5. Aves. Vertebrates clotlied with feathers (Birds). Subclass 1. Archwornithes. Birds having a prolonged tail of many verte- brae (Archfeopteiyx). Subclass 2. Xeornithes. Birds having the tail-vertebrae compacted into a pygostyle (Modern Birds).
Class 6. ^Mammalia. Vertebrates which suckle their voung, and are more or less clothed with hair (Mam- mals). Subclass 1. Prototlwria. Mammals with oviducts separated (Didelphia). Subclass 2. Theria. Mammals with ovi- ducts united for a longer or shorter part of their length ( Monodelphia ) . A. Metatheria. Voung born in rudimen- tary condition, and sheltered in a pouch (Marsupials). B. Euthcria. Voung born in a uterus; no pouch present (liigher Mammals).
Bibliography. In addition to works mentioned above, consult: Bronn (editor), Klassen und Ordnungen des Thierreichs (Leipzig and Heidelberg. 1859, et seq. ) ; Haeckel, Natürliche Schöpfungsneschichte (.Jena. 1808); Lankester, Xotes on Eiiihriiologif and Classification (Lon- don, 1877), and article "Zoology" in !)th cd. Enri/cloptrdia Britannica; Leunis, Si/nopsis der Thierknndc (Hanover. 1883-80): Huxley. An- atomy of Vertebrates (Xew Vork, 1878), and Anatomy of Invertebrated Animals (New York, 1888) : Standard Natural History (Boston, 1885) ; Lang, Text-book of Comparative An- atomy (London, 1891-96) ; Newton, Dictionary of Birds (London and New Vork. 1893-9G) ; Royal Natural History (London. 1805) ; Cambridge Natural History (Cambridge. Eng.. 1895, et seq.) ; Parker and Haswell, Text-book; of Zoölogy (London and New York, 1897) : Davenport, Introduction to Zoology (New York, 1900). See, also, books mentioned under Evolution; Embryology,' and such titles as Bird, Fish, Insect, etc., and under biographies of the naturalists above mentioined.
CLASSIFICATION OF SHIPS. See A1; and Lloyds.
