R.A.B. & Missing Horcrux

[georgy_grl]

No: HPFGUIDX 136940

In OotP, JKR refers to a "Heavy locket which none of them could open" 
in the chapter titled: "The Nole and Most Ancient House of Black.
Late in HBP, a fake horcrux is discovered, and the note inside the 
horcrux is signed R.A.B. R.A.B seems to have known Voldemort, very 
well, as only the Death Eaters (and occaisionally Dobby) refer to 
Voldemort as "The Dard Lord", and the note begins with: "To The Dark 
Lord".

I just wondered: what is Sirius' brother, Regalus' middle name, and 
couldn't JKR have described the locket more fully, or does anyone think 
that would have given away clues.

Georgy Granger