You will receive one share of Prothena for every 41 shares of Elan. So if you own 1000 shares of Elan you will receive 24 shares of PRTA. Also since the settlement date was Dec 14th you would have to have bought Elan no later then Dec 11th to qualify for free shares.
This has been running at 1-2 million shares daily, look at the History Yahoo. It runs 10 million today with a 50 cent gain. Word is getting out ELN as it stands now is for sale and moving forward. The mangement/board has their play toy to expense their lifestyles via Prothena and the scientists that have not truly produced since Tysabri was an offshoot of the AD drug development can continue playing in their backyard. ELN will finally be put out of its misery. The questions is how much will be paid for ELN.