** Cable networks co Versant Media Group's VSNT.O shares fall ~14% to $40 on first day of trading
** Comcast CMCSA.O completes spinoff of cable networks division into VSNT; includes channels such as CNBC and USA Network
** Existing CMCSA shareholders received one share of VSNT Class A or Class B common stock for every 25 shares of CMCSA Class A or Class B common stock, respectively
** Spinoff VSNT headed by Mark Lazarus as CEO
** Versant's assets generate ~$7 bln in annual revenue, co says
(Reporting by Anhata Rooprai in Bengaluru)
((Anhata.Rooprai@thomsonreuters.com))