Xenocrates
Ancient Greek Scientists: Xenocrates of Chalcedon, Biography.com: Xenocrates, Columbia Encyclopedia: Xenocrates, FOLDOC: Xenocrates, Life of Xenocrates, MacTutor History of Mathematics: Xenocrates of Ch, Wikipedia: Xenocrates, Xenocrates
Xenophanes of Colophon
Internet Encyclopedia of Philosophy: Xenophanes, The Homeric Gods and Xenophanes' Opposing The, Xenophanes of Colophon, Xenophanes: Fragments and Commentary