What are the strange property types generated in a C# anonymous type?

Observe the following trivial anonymous type in C#

new { X = 5 };

The respective compiler generated code as seen in Reflector (omitting the object method overrides) is:

[CompilerGenerated]
internal sealed class <>f__AnonymousType0<<X>j__TPar>
{
    // Fields
    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
    private readonly <X>j__TPar <X>i__Field;

    // Methods
    [DebuggerHidden]
    public <>f__AnonymousType0(<X>j__TPar X)
    {
        this.<X>i__Field = X;
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    // Properties
    public <X>j__TPar X
    {
        get
        {
            return this.<X>i__Field;
        }
    }
}

My question is WOE (What On Earth) is <X>j__TPar? The type is reflected nowhere in Reflector (pun intended).

<X>j__TPar is the name of the generic argument used in the <>f__AnonymousType0 type definition. A bit less readable indeed than T but guaranteed to never collide with another name.