Stheno
In Greek mythology, Euryale ( yoor-EYE-ə-lee; Ancient Greek: Εὐρυάλη, romanized: Euryálē, lit. 'far-roaming') and Stheno ( or ; Greek: Σθενώ, translit. Sthenṓ, lit. "forceful") were two of the three Gorgons sisters, including Medusa, who were able to turn anyone who looked at them to stone.
Family
According to Hesiod, and Apollodorus, Euryale and Stheno, along with Medusa, were daughters of the primordial sea-god Phorcys and the sea-monster Ceto, while, according to Hyginus, they were daughters of Gorgon, an offspring of Typhon and Echidna, and Ceto. Euryale may possibly be the mother of Orion as some sources list Euryale as his mother, but doesn't always specify whether it is the Gorgon or the daughter of Minos.
Mythology
Euryale and Stheno were immortal, whereas Medusa was mortal. According to Apollodorus' version of their story, Euryale and Stheno, along with Medusa had the ability to turn to stone anyone who looked upon them. And when Perseus managed to behead Medusa by looking at her reflection in his bronze shield, Euryale and Stheno chased after him, but were unable to see him because he was wearing Hades' cap, which made him invisible.
Euryale's lamenting cry, while chasing Perseus, is noted in two sources. In one of Pindar's victory odes, the poet has Athena create the "many-voiced songs of flutes" to imitate the "shrill cry" of the "fast-moving jaws of Euryale". While Nonnus, in his Dionysiaca, has the fleeing Perseus "listening for no trumpet but Euryale's bellowing".