Achelous
2 of the 7 encyclopedias on this shelf carry an entry for Achelous. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
ak-e-lo'us, in Greek mythology, a river god, son of Oceanus and Tethys, and the eldest of their three thousand sons. He fought with Hercules for the favor of Dejanira. Hercules was victorious. When he saw that he was in danger, Achelous changed himself into the form of a snake. Hercules exclaimed, "It was the labor of my infancy to conquer snakes," and clasped the neck of the snake in his strong hands. Achelous was nearly strangled, and quickly assumed the form of a bull. Hercules threw his arms about the bull's neck, and, drawing its head to the ground, overthrew the animal upon the sand. He then grasped the horn of the bull and tore it from its head. This horn was consecrated by the Naiades, and was called Cornucopia and regarded as the symbol of Plenty, but Achelous fought no more with Hercules. See Amalthea ; Hercules
1000 Classical Characters (1900)
A river of Epirus, which rises in Mt. Pindos and, flowing between Acarnania and Aetolia , empties into the Gulf of Corinth. Achelous is also the name of the deity of the river Achelous, who is said to have contended with Hercules for the hand of Deianira, but, although he changed himself into the form of a bull, he was defeated by the hero in the contest and deprived of one of his horns, which, however, he recovered by giving up the horn of Amalthea. The Achelous was reverenced by the ancients as a stream of great antiquity and was regarded as the general representative of all fresh waters, so that we find in Vergil the expression Acheloia pocula, meaning water in general.