Updated from 9:13 a.m. EDTEarnings at investment firm Jefferies ( JEF) rose 28% in the second quarter, but the results were less than what many on Wall Street were anticipating. In the quarter, the firm earned $45.6 million, or 32 cents a share, up from $35.4 million, or 26 cents a share, in the year-ago period. Net revenue at Jefferies rose 18% to $327 million. But earnings and revenue fell short of analyst estimates, according to Thomson Financial. The analyst consensus had Jefferies earning 33 cents in the quarter on net revenue of $348.4 million. The stock fell precipitously on the news, losing $1.75, or 6.8%, to $23.95. At its low point of the session, $21.45, the stock was down 16.5% from Monday's close. Jefferies, unlike other bigger Wall Street firms, did not see a huge gain in trading-related revenue in the quarter. Revenue from principal transactions, which includes trading revenue, rose a modest 11% to $94 million. Investment banking revenue rose 20% to $122.9 million. Commission revenue, from customer trading, rose 22% to $71.6 million. The big revenue driver for Jefferies in the quarter was interest earned on customer margin balances. Interest on the accounts of customers trading with the house's money more than doubled to $138.8 million. The Federal Reserve's continued raising of short-term interest rates has been a boon to many Wall Street firms. The interest firms charge to customers who trade with borrowed money is pegged to hikes in short-term rates.