The species Pterophyllum altum only occurs in its natural form, silver with black/brown vertical bars. It may be distinguished from the other two species by the sharper incline of the front of the head, the dorsal line, and a more pronounced dip or notch above the nose; I'm attaching an illustration of this which I assume is accurate, though I cannot now remember where I found this some years ago. Also, the white space between the vertical bars is narrow than the bars themselves; the bars are more brownish and the intermediate bars are more prominent than on P. scalare. I'm also attaching a couple photos of P. altum, the second by Jan Sevcik is easier to ID. This is the largest of the three angelfish species at maturity.
I should also mention that there is an angelfish in the trade now that is often referred to by the common name as "Peruvian Altum" angelfish. This is almost certainly not the species P. altum but actually P. scalare although it has something of a different body form. The shape around the head is thought to not be reliable by some, so it may be best to examine the vertical stripes.
Byron.
