What is the 'X' below the Lunar X ?

[stevend]

While I was watching the Lunar X develop on saturday night, I noticed that below it, also right on the terminator was another x, a more curved one (like we would use in algebra at school). It was lovely seeing the two at the same time. It was clearly another clair-obscur (I can use wikipedia, ) effect and almost certainly caused by shadows along the edges of two close together craters.

Does this other 'x' have a name ?

Thanks

Steven