Biserial fins are typical of keratosis (an extinct genus of bipedal fish). The paired fins of Porolepis (extinct genus of porolepiform sarcopterygian fishes) are similar to the biserial archipterygium: their skeleton is a long, segmented axis with thinner rays radiating from the front and back. The fin is muscular, strong but very flexible. 

This fin is equipped with a muscular "rigging", but thin and flexible, allowing it not only to rest on the bottom, but also to palpate the surrounding space, working with the organ of touch.