Page:Popular Science Monthly Volume 3.djvu/450

436 forward. The front is about one-third the size of this large hind-foot, and the toes are arranged like those of the front-feet of the Herpetoids. One of the species seems to have had a long, slender tail. This batrachian must have been as large as an elephant, and exceeded in size every other animal among the Ichnozoa. Imagine a frog as large as an elephant, whether announcing the advent of spring by piping, croaking at night in the summer, or taking gigantic leaps after the manner of his modern representatives!

A very important character in the feet of frogs is the possession of pellets, or knobs, instead of claws, at the ends of the toes. These may be observed in the Otozoum, and all the other genera of this group. One genus resembles the Cheirotherium in form, but not in size, having a foot less than an inch long. None have the remarkably long middle toes on the hind-foot, so characteristic of living frogs.

A small, living salamander has the posterior feet pointing back-ward; and, as he walks, the toes point away from the head. The track-way, therefore, consists of two parallel rows of footprints, half of each pointing forward and half directed backward. This salamander has its representative ichnozoan in the Stetiodactylus, not varying essentially in size from it.

One of the most interesting classes of batrachian impressions is called Batrachoides. They consist of numerous saucer-shaped hollows an inch in diameter, crowded together so thickly that the original oval outlines have become pentagonal. Not unfrequently these saucers are arranged in lines and squares, because parallel rows of ripple-marks were occupied by the animals in their construction, often covering several square yards of surface.



Whether arranged in order or clustered helter-skelter, these impressions cannot be distinguished from the mud-nests made every summer by existing tadpoles. Hence it is natural to suppose that the markings made at the different periods were produced by the same agency; and, as we know the origin of the latter, we may infer how the first came upon the rocks. The chief difficulty in the way of accepting this view lies in the perfect resemblance between them. If this doctrine is received, we must believe in the existence of tadpoles in the carboniferous rocks, because they contain similar relics. Those in the Triassic are remarkably distinct, making most beautiful specimens for the show-case.

The reference of the next group to the class of fishes may excite