R is surprisingly tricky for musical instruments, so I'm gonna do two in a row again because no one seems to be jumping in.
Rumba Box - A thumb piano (mbira) in the low bass register. It basically looks like a large wooden box that has a row of metal flappers on it, which, when struck, sound sort of like an upright bass. You play it by sitting on it and plucking the flappers. It's common in early (pre-reggae) Jamaican folk music, though it's from Africa originally, where thumb pianoes are common. It's also sometimes called the marimbula.
Here's a pic (from my favorite instrument store, Lark in the Morning.... order a free catalog from them, they're sooooo neat!):http://larkinthemorning.com/product.asp_Q_pn_E_MAR173_A_Marimbula_E_
Okay, now "S" should be pretty easy....