It seems to have been assumed that Lucretius elides final s promiscuously, as Ennius does, at any part of the line. The following statement of facts will show that the truth is very different: I take all cases where the reading appears certain. (1) He has twenty-eight such elisions at the end of the fifth foot, including the emended ii. 623, 975, 986, v. 1410; (2) ten at the weak caesura of the fifth foot, including the emended iii. 198, 1016, v. 949, 1106. But except in these two positions the elison is quite rare and exceptional. I will begin the exceptions by giving (3) a peculiar group: ii. 5, omm' sit. 458, omnibu' sunt (Lamb.), 1079, aliquoiu' siet (Gronov.), iv. 493, coloribu' sint, 1152, corpori' sunt, 1268, opu' sunt, v. 456, minoribu' sunt, 1445, priu' sunt; all these are from the first four feet, but evidently to Lucretius a combination like opu' sunt is very different from, say, opu' fit. Indeed, I take it that opusit was to him just one word like necessest; the following s in sit and sunt helps, perhaps, and so the solitary instance in Catullus is before s; at any rate, this group is obviously exceptional. There remain (4) only two elisions at the end of the fourth foot, iv. 1035 and the emended vi. 972; two at the end of the second foot, immutabili' in i. 591, and immortalibu' in v. 53, both due to correctors and both words of a form which is rare at the opening of a line; one in weak fourth caesura, iii. 905; one at end of first foot, i. 978. You will hardly believe me, but those are all.