70 THE OLD RED SANDSTONE. 
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 con- 
dition of the Osteolepis, and many of itscontemporaries. The 
enamelled teeth were placed in jaws which presented outside 
a surface as naked and as finely enamelled as their own. 
(See Plate IV., fig. 5.) The entire head was covered with 
enamelled osseous plates, furnished inside like other bones, as 
shown by their cellular construction, with their nourishing 
bloodvessels, and perhaps their oil, and which rested apparent- 
ly 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 skele- 
tons, 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 support- 
ing bones or rays seem to have been connected laterally 
by the membrane; but on both sides they presented bony 
and finely enamelled surfaces. (See Plate IV., fig. 6.) 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 orof plates, of scales or of rays, presented 
an external surface of enamel. 
