Shares of Barnes & Noble are tumbling to all-time lows after airing some ugly holiday sales numbers.

The beleaguered bookseller said Friday that comparable-store sales slid 6.4 percent during the crucial nine-week period ending Dec. 30.

Most retailers have strengthened digital operations and their sales have followed. At Barnes & Noble, however, online sales dropped 4.5 percent.

Amazon.com is winning over more people each year to its Prime membership program, at one point handing out trial memberships to 4 million people in one week this holiday. That's proven devastating for Barnes & Noble, where overall holiday sales fell 6.4 percent, to $953 million.

The company says trends of improving sales leading into November began to fade by December.

Shares of Barnes & Noble Inc. fell 15 percent, to $5.52.