Unknown small Spondylus

[diocrisseashells1000]

Hi Emma,
it is not easy to id that specie, i also have 2 of that kind (upper valve only) and it is also 24mm. and less. there are only 3 options i have in my mind and that is S.squamosus, S, zonalis, and S.sinensis, But i am leaning more on S.squamosus, cause it is more variable in shape and colourations....but  the size is giving me doubt..... i would like to help you more  but we are both in the same situation. :-[