Looks like a high-tech skateboard to me. 
For the aviation enthusiasts, here are some more: http://www.aviationpics.de/mystery/page_01.htm
It was originally supposed to protect the mighty B-36. This from the Air Force Museum web page:
"Another EB-29 was used carry the XF-85 and test the parasite fighter concept. The XF-85 "Goblin" parasite aircraft was developed to protect B-36 bombers flying beyond the range of conventional escort fighters. In theory, a B-36 penetrating enemy territory would carry its protecting fighter in the bomb bay. If attacked by enemy aircraft, the bomber would lower the Goblin on a trapeze and release it to combat the attackers. After the enemy had been driven away, the parasite fighter would return to the bomber, hook onto the trapeze, fold its wings, and be lifted back into the bomb bay. Although the XF-85 was successfully launched and retrieved from an EB-29B on several test flights, it was never flown from a B-36. The test program was canceled in late 1949 when mid-air refueling of fighter aircraft for range extension began to show greater promise."
I believe they display it under the B-36 which sits INSIDE the Air Force Museum in Dayton (they built the building around its 230' wing span...they are soon going to take out the walls to move it to yet another building).
The B-36 is my all-time favorite airplane. What a beautiful rumbling beast. It is shown in all of its VistaVision glory in the film STRATEGIC AIR COMMAND.
Here (from the USAF Museum web page) are the specs:
SPECIFICATIONS
Span: 21 ft. 1 in.
Length: 14 ft. 1 in.
Height: 8 ft. 3 in.
Weight: 4,550 lbs.
Armament: Four .50-cal. machine guns
Engine: One Westinghouse XJ-34 of 3,000 lbs. thrust
Crew: One
PERFORMANCE
Maximum speed: 650 mph.
Combat speed: 581 mph.
Maximum endurance: 1 hr. 20 min.
Combat Ceiling: 46,750 ft.