A book’s index can entertain as well as inform, and in D. J. Taylor’s Lost Girls, a lively, perceptive, and gossip-strewn inquiry into an overlooked aspect of an influential corner of London’s literary life in, mainly, the 1940s, the index does not disappoint. Turning from “Horizon, ‘bugger incident,’ ” to the entries for that storied magazine’s creator and presiding genius, “Connolly, Cyril,” we find, among other accolades, “capriciousness,” “dilettante quality,” “double standards and hypocrisy,” “mother-fixation,” “self-absorption,” “self-destructiveness,” “self-propagating mystique,” “sulkiness,” “tactlessness,” and, in a final jab of the indexer’s finger, “vacillation and procrastination.”