Pterophyllum scalare
Pterophyllum altum
They're two different species.
Scalare is the one you see in fish stores, which has been bred into a number of varieties. This is the species that's commonly associated with the term "Angelfish".
Altum is a larger species which is rarely seen in fish stores, and unlike scalare, is caught from the wild and not widely bred in captivity. They're also more fragile then scalare, requiring lower pH (6.4 and lower) and higher temperatures ( 82 +).
I think ... Altum are the silver/black 4-barred, longer bodied angelfish, and they are mostly wild caught. Scalare are various colored - black/white/marbled/koi (yellow) and shorter bodied. Mostly aquarium raised. Altum are more sensitive to water conditions (softer lower ph), and scalare have adapted to common household water condition through longtime aquarium breeding. That is what I think I know.:)
Pterophyllum scalare are a domestic Angelfish, captive bred. Not too sensitive, easy to keep. Cost little.
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Pterophyllum altum are wild Angelfish, wild caught. Very sensitive and difficult to keep. Will put you in the poor house.
The Pterophylum altum is almost identical with Scalare except Altum can have more stripes.
