A filing with the the U.S. Securities and Exchange Commission by public listed electric car maker Tesla has shed some light on future plans. There will be a prototype of a Model X crossover by the end of the year, and the company will end production of the Tesla Roadster in December this year, concentrating on a new platform series. Tesla has delivered 1,650 Roadsters to customers in over 31 countries to date.

According to Tesla, it is “designing the Model X to incorporate the functionality of a minivan with the consumer appeal of a sports-utility vehicle.” CEO Elon Musk has previously revealed in an interview that the Model X will debut in 2014.

When pitching to investors for its IPO last summer, Tesla said it wanted to build four derivatives from the Model S platform. First out will be a midsize sedan (the car pictured here, click here for gallery and video) followed by a convertible, a van and a crossover/SUV. From the latest plans, it looks like the latter two will be combined into one Model X.

As for the upcoming Model S sedan, customer deliveries are scheduled to start in mid-2012 and that there are several drivable prototypes already complete. Tesla is planning to make about 20,000 Model S per year, with prices ranging from $57,400-$77,400. As of end April 2011, the company has collected around 4,600 bookings with a minimum refundable payment of $5,000, the filing said.

“We anticipate that the initial units of the Model S will be introduced with a Signature Series, which will have range capability of 300 miles (480 km) and include certain colors and options, some of which may not be available in the general production of the Model S. We also plan to offer the capability to fast charge in as little as 45 minutes and the ability to rapidly swap out its battery pack at commercial charging stations,” it was revealed.