Sentence:  Apollonius ... by some probable conjectures, found her out to be a serpent, a <WSD>lamia</WSD>, and that all her furniture was like Tantalus' gold described by Homer, no substance, but mere illusions. 
Meaning of the word marked with <WSD> tags:  A monster preying upon human beings and who sucked the blood of children, often described as having the head and breasts of a woman and the lower half of a serpent.