Passage 3.19.3
τοῦ δὲ ἀγάλματος τὸ βάθρον παρέχεται μὲν βωμοῦ σχῆμα, τεθάφθαι δὲ τὸν Ὑάκινθον λέγουσιν ἐν αὐτῷ, καὶ Ὑακινθίοις πρὸ τῆς τοῦ Ἀπόλλωνος θυσίας ἐς τοῦτον Ὑακίνθῳ τὸν βωμὸν διὰ θύρας χαλκῆς ἐναγίζουσιν· ἐν ἀριστερᾷ δέ ἐστιν ἡ θύρα τοῦ βωμοῦ. ἐπείργασται δὲ τῷ βωμῷ τοῦτο μὲν ἄγαλμα Βίριδος, τοῦτο δὲ Ἀμφιτρίτης καὶ Ποσειδῶνος· Διὸς δὲ καὶ Ἑρμοῦ διαλεγομένων ἀλλήλοις πλησίον Διόνυσος ἑστήκασι καὶ Σεμέλη, παρὰ δὲ αὐτὴν Ἰνώ.
The pedestal of the statue has the shape of an altar, and it is said that Hyacinthus is buried within it. At the festival of the Hyacinthia, before sacrificing to Apollo, they make offerings through a bronze door on this altar to Hyacinthus; this door is situated on the left side of the altar. On the altar there are carved figures: one image of Biris, another of Amphitrite and Poseidon, and near them Zeus and Hermes conversing with each other; close by stand Dionysus and Semele, with Ino beside Semele.