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Share capital is what you pay when you incorporate the company and shows on the balance sheet that way, it cannot officially be paid or registered with the Registrar of Companies if it is denominated in BTC.
"Share capital or capital stock (US English)[1] refers to the portion of a company's equity that has been obtained (or will be obtained) by trading stock to a shareholder for cash or an equivalent item of capital value. For example, a company can issue shares in exchange for computer servers, instead of purchasing the servers with cash."
http://en.wikipedia.org/wiki/Share_capitalAgain, wut?