The fishes of the Wealden belong partly to the genera _Pycnodus_ and _Hybodus_ (see figure of genus in Chap. XXI.), forms common to the Wealden and Oolite; but the teeth and scales of a species of _Lepidotus_ are most widely diffused (see fig. 236.). The general form of these fish was that of the carp tribe, although perfectly distinct in anatomical character, and more allied to the pike. The whole body was covered with large rhomboidal scales, very thick, and having the exposed part covered with enamel. Most of the species of this genus are supposed to have been either river fish, or inhabitants of the coasts, having not sufficient powers of swimming to advance into the deep sea. [Illustration: Fig. 237. _Corbula alata_, Fitton. Magnified.] The shells of the Hastings beds belong to the genera _Melanopsis_, _Melania_, _Paludina_, _Cyrena_, _Cyclas_, _Unio_, and others, which inhabit rivers or lakes; but one band has been found in Dorsetshire indicating a brackish state of the water, and, in some places, even a saltness, like that of the sea, where the genera _Corbula_ (see fig. 237.), _Mytilus_, and _Ostrea_ occur. At different heights in the Hastings Sand, in the middle of the Wealden, we find again and again slabs of sandstone with a strong ripple-mark, and between these slabs beds of clay many yards thick. In some places, as at Stammerham, near Horsham, there are indications of this clay having been exposed so as to dry and crack before the next layer was thrown down upon it. The open cracks in the clay have served as moulds, of which casts have been taken in relief, and which are, therefore, seen on the lower surface of the sandstone (see fig. 238.). [Illustration: Fig. 238. Underside of slab of sandstone about one yard in diameter. Stammerham, Sussex.] Near the same place a reddish sandstone occurs in which are innumerable traces of a fossil vegetable, apparently _Sphenopteris_, the stems and branches of which are disposed as if the plants were standing erect on the spot where they originally grew, the sand having been gently deposited upon and around them; and similar appearances have been remarked in other places in this formation.[230-A] In the same division also of the Wealden, at Cuckfield, is a bed of gravel or conglomerate, consisting of water-worn pebbles of quartz and jasper, with rolled bones of reptiles. These must have been drifted by a current, probably in water of no great depth. [Illustration: Fig. 239. _Sphenopteris gracilis_ (Fitton), from near Tunbridge Wells. _a._ portion of the same magnified.]