2. Basic and Diluted Net Loss per Common Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common share equivalents outstanding for the period that are determined to be dilutive. Common stock equivalents are primarily comprised of preferred stock, warrants for the purchase of common stock and stock options. For the three months ended March 31, 2019, there is no difference in the number of shares and net loss used to calculate basic and diluted shares outstanding because their effect would have been anti-dilutive. The Company had potentially dilutive securities, shares of common stock, totaling approximately 22.2 million and 1.6 million as of March 31, 2019 and 2018, respectively.

Below are basic and diluted loss per share data for the three months ended March 31, 2018, which are in thousands except for share and per share data: