Passage 7.19.4
καταφυγόντων δὲ αὐτῶν ἐπὶ χρηστήριον τὸ ἐν Δελφοῖς, ἤλεγχεν ἡ Πυθία Μελάνιππον καὶ Κομαιθώ· καὶ ἐκείνους τε αὐτοὺς μάντευμα ἀφίκετο θῦσαι τῇ Ἀρτέμιδι καὶ ἀνὰ πᾶν ἔτος παρθένον καὶ παῖδα οἳ τὸ εἶδος εἶεν κάλλιστοι τῇ θεῷ θύειν. ταύτης μὲν δὴ τῆς θυσίας ἕνεκα ὁ ποταμὸς ὁ πρὸς τῷ ἱερῷ τῆς Τρικλαρίας Ἀμείλιχος ἐκλήθη·
When they sought refuge at the oracle at Delphi, the Pythia revealed the guilt of Melanippus and Comaetho. An oracle came to these people themselves, commanding them to sacrifice to Artemis and, every year thereafter, to offer the goddess as sacrifice a maiden and a youth who were most beautiful in appearance. Indeed, because of this sacrifice, the river near the temple of Triclaria received the name Ameilichus ("Relentless").