Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Ecstored outline of a fish of the genus Palceoniscus, Agass. Palceothrissum, Blainville. The PalcBoniscus above mentioned belongs to that division of fishes which M. Agassiz has called ' Heterocercal,' which have their tails unequally bilobate, like the recent shark and sturgeon, and the verte- bral column running along the upper caudal lobe. (See fig. 500.) Fig. 500. Fig. 501. Shark. Heterocercal. Shad. (Chipea.
Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Ecstored outline of a fish of the genus Palceoniscus, Agass. Palceothrissum, Blainville. The PalcBoniscus above mentioned belongs to that division of fishes which M. Agassiz has called ' Heterocercal,' which have their tails unequally bilobate, like the recent shark and sturgeon, and the verte- bral column running along the upper caudal lobe. (See fig. 500.) Fig. 500. Fig. 501. Shark. Heterocercal. Shad. (Chipea. Herring tribe.) Homocercal. The ' Homocercal' fish, which comprise almost all the 9000 species at. present known in the living creation, have the tail-fin either single or equally divided; and the vertebral column stops short, and is not prolonged into either lobe. (See fig. 501.) Now it is a singular fact, first pointed out by Agassiz, that the heterocercal form, which is confined to a small number of genera in the existing creation, is universal in the magnesian limestone, and
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