on putrid vegetables and animal substances at the bottom; hence they have constant occasion to keep their bodies in the same inclined position as the extinct fossil Fishes, whose feeble brush-like teeth show that they also fed on soft substances in similar situations.[1]
The Sharks employ their tail in another peculiar manner, to turn their body in order to bring the mouth, which is placed downwards beneath the head, into contact with their prey. We find an important provision in every animal to give a position of ease and activity to the head during the operation of feeding.[2]
Fishes of the Magnesian Limestone, or Zechstein.
The Fishes of the Zechstein at Mansfeld and Eisleben have been long known, and are common in all collections; figures of many species are given by M. Agassiz. Examples of the Fishes of the Magnesian limestone of the north of England, are described and figured by Professor Sedgwick, in the Geol. Trans(of London, (2d Series, Vol. iii. p. 117, and Pl. 8, 9, 10.) He states in this paper (p. 99,) that the occurrence of certain Corals and Encrinites, and several species of Producta, Arca, Terebratula, Spirifier, &c. shows that the Magnesian limestone is more nearly allied in its
- ↑ At the siege of Silistria, the Sturgeons of the Danube were observed to feed voraciously on the putrid bodies of the Turks and Russian soldiers that were cast into that river.
- ↑ This remarkable elongation of the superior lobe of the tail is found in every bony Fish of strata anterior to and including the Magnesian limestone; but in strata above this limestone the tail is regular and symmetrical. In certain bony Fishes of the secondary period, the upper lobe of the tail is partly covered with scales, but without vertebra. The bodies of all these Fishes also have an integument of rhomboidal bony scales, covered with enamel.
No species of Fish has been found common to the Carboniferous group, and to the Zechstein or Magnesian limestone; but certain genera occur in both, e. g. the genus Palæoniseus and Polypterus.
