I cannot trace the reference; and it seems unlikely that if it existed it should have escaped the knowledge of Professor Munro, who, in his note to the passage quoted from Lucretius (vi. 786), cites similar references in Plutarch and Dicaearchus, but says nothing of Diodorus. The marginal note in the original edition has only 'Lib.' Swift probably trusted to his memory, intending subsequently to verify the quotation and fill in the number of the Book, and then forgot to do so. After the MS. was in the printer's hands, he cared no more about it.