This page needs to be proofread.
50
Fishes.
able in the genus Lepisosteus[1] of Lacepède, the bony pikes, five of which inhabit the rivers of America. The Osteolepis or bony-scale fish, and other fishes of the old red sandstone, seem to carry this extraordinary character to a greater extreme.
"We are accustomed to see vertebrated animals with the bone uncovered in one part only,—that part the teeth,—and with the rest of the skeleton wrapped up in flesh and skin. Among the reptiles we find a few exceptions; but a creature with a skull as naked as its teeth,—the bone being merely covered, as in these, by a hard shining enamel, and with toes also of bare enamelled bone, would be deemed an anomaly in creation. And yet such was the condition of the Osteolepis, and many of its co temporaries. The enamelled teeth were placed in jaws which presented outside a surface as naked and as finely enamelled as their own. The entire head was covered with enamelled osseous plates, furnished inside like other bones, as shown by their cellular construction, with their nourishing blood-vessels, and perhaps their oil, and which rested apparently on the cartilaginous box, which must have enclosed the brain, and connected it with the vertebral column. I cannot better illustrate the peculiar condition of the fins of this ichthyolite, than by the webbed foot of a water-fowl. The web or membrane in all the aquatic birds with which we are acquainted, not only connects, but also covers the toes. The web or membrane in the fins of existing fishes accomplishes a similar purpose; it both connects and covers the supporting bones or rays.—Imagine, however, a webbed foot in which the toes—connected but not covered—present, as in skeletons, an upper and under surface of naked bone; and a very correct idea may be formed from such a foot, of the condition of fin which obtained among at least one half the ichthyolites of the Lower Old Red Sandstone. The supporting bones or rays seem to have been connected laterally by the membrane; but on both sides they presented bony and finely-enamelled surfaces. In this singular class of fish, all was bone without, and all was cartilage within; and the bone in every instance, whether in the form of jaws or of plates, of scales or of rays, presented an external surface of enamel."—p. 99.
"The Osteolepis was cased, I have said, from head to tail, in complete armour.—The head had its plaited mail, the body its scaly mail, the fins their mail of parallel and jointed bars; the entire suit glittered with enamel; and every plate, bar and scale was dotted with microscopic points. Every ray had its double or treble punctulated row, every scale or plate its punctulated group; the markings lie as thickly in proportion to the fields they cover, as the circular perforations in a lace veil; and the effect, viewed through the glass, is one of lightness and beauty. In the Cheirolepis an entirely different style obtains. The enamelled scales and plates glitter with minute ridges, that show like thorns in a December morning varnished with ice. Every ray of the fins presents its serrated edge, every occipital plate and bone its sculptured prominences, every scale its bunch of prickle-like ridges. A more rustic style characterized the Glyptolepis. The enamel of the scales and plates is less bright; the sculpturings are executed on a larger scale, and more rudely finished. The relieved ridges, waved enough to give them a pendulous appearance, drop adown the head and body. The rays of the fins, of great length, present also a pendulous appearance. The bones and
- ↑ The name is altered to Lepidosteus by Agassiz: the genus Polypterus of Agassiz found in the Nile and Senegal, has similar characters.
