162 ICHTHYOLOGY raals. The following have been the principal cultivators of this science in America : Dr. Samuel L. Mitchill published in vol. i. of the " Transactions of the Literary and Philosophi- cal Society of New York" (1815) a history of 149 species of New York fishes, with many il- lustrations ; he adopts the Linnsean system ; other descriptions of his species are in the "Proceedings of the Philadelphia Academy" and in the " Annals of the Lyceum of Natu- ral History of New York." Lesueur has de- scribed and exactly figured many species in the Philadelphia academy's "Proceedings." Rafinesque published in the same work, and in his Ichthyologia Ohiensis (1820), descrip- tions of many species which had escaped his predecessors. Dr. Kirtland (1838) described the fishes of the Ohio river, and Dr. Holbrpok several years later those of South Carolina. Dr. De Kay in 1842, in his "Zoology of New York," divides fishes into bony and cartilagi- nous, the former having the sections: 1, pee- tinibrancMi, with spiny-rayed and soft-rayed abdominal, subbrachial, and apodal orders ; 2, lophobrancJM, and 3, plectognathi ; the latter include the sections eleutheropomi, plaglosto- mi, and eyolostomi. Dr. D. H. Storer, in his "Report on the Fishes of Massachusetts" (1839), and in the illustrated edition of the same in the " Memoirs of the American Acad- emy" (1855-'60), and also in his "Synopsis of the Fishes of North America" ("Memoirs of the American Academy," vol. ii., 1846), fol- lows the arrangement of Cuvier. These works are of great value to the student of North American ichthyology. The Wilkes, North Pacific, and Japan expeditions sent out by the United States government, and the various ex- plorations by land for the survey of the Mex- ican boundary, the Pacific railroad route, and military and civil roads, have added largely to the materials, both foreign and native, at the disposition of American ichthyologists; these have been worked up principally by Messrs. Baird and Girard of the Smithsonian institu- tion, where the collections are deposited. The results are published in the government re- ports on the naval expeditions, in vol. x. of the " Pacific Railroad Reports," in vol. ii. of the "Mexican Boundary Survey," and in the publications of the Philadelphia academy. The disposition to make new genera and subdi- vide old ones is carried to a puzzling extreme in ichthyology as well as in other departments of zoology ; and the prevalent system of placing the name of the genus maker after the species, by whomsoever and whenever described, offers a premium for naturalists to make the greatest number possible of new genera. In getting rid of the too great condensation of Linnaeus, naturalists have fallen into the worse extreme of too extensive subdivision. For details on the structure and physiology of fishes, see FISHES. FOSSIL ICHTHYOLOGY. Fishes are by far the most numerous of the vertebrates found in the strata of the earth, extending ICHTHYOSAURUS from the Silurian epoch to the tertiary ; their number, excellent state of preservation, and remarkable forms, render fossil fishes of great interest in explaining the changes of our plan- et's surface, and in completing the chain of ichthyic relations. The classic work on fossil fishes is the Recherches sur les poissonsfosgiles, by Prof. Agassiz (1833-'43) ; in this magnifi- cent work about 1,000 species are described, with accurate and elegant illustrations, the re- sult of his examinations of more than 20,000 specimens in the cabinets of Europe. lie di- vides fossil fishes into the four orders of ga- noids, placoids, ctenoids, and cycloids, accord- ing to the structure and form of the scales, these portions of the external skeleton being generally well preserved ; the orders he divides into families according to the structure and po- sition of the fins, the form of the bones of the head and of the teeth, and the structure of the gill covers and of the spinous fin rays. His classification is as follows : order I., ganoidei, characterized by osseous plates covered with enamel (see GANOIDS) ; order II., placoidei, with tabular scales, like sharks and rays ; or- der III., ctenoidei, having many living repre- sentatives, with scales serrated on their poste- rior margins ; order IV., cycloidei, with ellip- tical or circular scales without serrations. The first order is most abundant from the old red sandstone to the chalk formation ; the second extends from the Silurian through the tertiary epochs ; the last two are not found anterior to the chalk, from which they extend through the tertiary strata. For details on fossil fishes, see the geological works of Hugh Miller. ICHTHYOSAURUS (Gr. !*%, fish, and aavpo?, lizard), a gigantic fossil marine reptile, belong- ing to the order enaliosaurians of Conybeare. The body was fish-like in form, with a large head, neck of equal width with occiput and thorax; the vertebras had biconcave articular surfaces, as in fishes and the perennibranchiate reptiles; the paddles, four in number, were comparatively small, resembling in form those of cetaceans, but in the number of digits and of their constituent bones and appended bifur- cated rays they came near the structure of the fins of fishes ; the tail was long, the vertebra gradually becoming smaller and flatter toward the end, and probably margined with a tegu- mentary fin expanded or in a vertical direc- tion ; the tail was doubtless the principal organ of locomotion, and presented the saurian char- acter of length and gradual diminution, being cetacean in its partially tegumentary nature, and fish-like in its vertical position. Accord- ing to Dr. Buckland, the skin was scaleless and finely wrinkled, as in cetaceans. The skull is like that of the dolphin, with a smaller cere- bral cavity and an unanchylosed condition of the cranial bones ; the intermaxillaries are greatly developed, and the orbits immense, sur- rounded by numerous large sclerotic plates ; in the convex articulating surface of the occiput, the solid structure of the back part of the skull,
