Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/216

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I select the genus Amblypterus (Pl. 27.,) as an example of Fishes whose duration was limited to the early periods of geological Formations; and which are marked by characters that cease after the deposition of the Magnesian limestone.

This genus occurs only in strata of the Carboniferous order, and presents four species at Saarbruck, in Lorraine; it is found also in Brazil. The character of the teeth in Amblypterus, and most of the genera of this early epoch, shows the habit of these Fishes to have been to feed on decayed sca-weed, and soft animal substances at the bottom of the water: they are all small and numerous, and set close together like a brush. The form of thebody, being not calculated for rapid progression, accords with this habit.

The vertebral column continues into the upper lobe of the tail, which is much longer than the lower lobe, and is thus adapted to sustain the body in an inclined position, with the head and mouth nearest to the bottom.

Among existing cartilaginous Fishes, the vertebral column is prolonged into the caudal tin of Sturgeons and Sharks: the former of these perform the office of scavengers, to clear the water of impurities, and have no teeth, but feed by means of a soft leather-like mouth, capable of protrusion and contraction,