With the Asian Knife species, you got:
Chitala Chitala and Chitala Ornate aka Clown Knives
Chitala Lopis aka Giant Knife or Spotless Clown Knife
Notopterus Notopterus aka Black Knife, Bronze Knife, or Asian Feather Fin
I believe that Notopterus Chitala is an older name for Chitala Chitala. They were reclassified and Chitala got their own Genus.
While there is a slight variation between C. Chitala and C. Ornate, it's basically unnoticable to the averge aquarist.
Then you have the African species, you got:
Papyrocronus Afer aka Spotted African Knife
Xenomystus Nigri aka African Knife
All of which are in the Notoperidae Family.