It appears to be an L-Type. Probably L1 given the size of the chuck. L00 and L0 were other common L-type sizes.
To remove it, there's usually a special wrench that fits that ring collar. Many lathes used this mechanism (especially LeBlond's) and it was gradually replaced with the D-type in the 1940s and 50s (roughly).
I don't have recent experience with these (I used a L0 in my teenage years but, didn't change the chuck very often) but think they're just fine. The only slight problem is finding backplates as not too many places make them -but they can be found.
Ray