This is the cover to Planet of the Apes #NN[18]:
The cover image is a composite of two panels. The main image is from the first panel on page 41 of this issue:
As per the 125% bromide note above the image has been enlarged, and otherwise modified (the ape's spear is closer to Derek on the cover image than in the original panel).
The second image of the gun wielding ape is from the last panel in Planet of the Apes #9 page 27:
The story contents are as follows:
Kingdom On An Island Of The Apes Chapter 1: The Trip
[Kingdom On An Island Of The Apes] Chapter 2: Arrival
Kingdom On An Island Of The Apes Part II Chapter 3: The City!
[Kingdom On An Island Of The Apes] Chapter 4: The Island Out of Time
[Kingdom On An Island Of The Apes] Chapter 5: Battle
According to the GCD, Kingdom On An Island Of The Apes was originally intended for an Annual, but was reformatted for publication in two consecutive issues. For this reason, Chapter 3 is also the beginning of Part II.
Kingdom On An Island Of The Apes had previously been published by Newton in Planet of the Apes #'s 11-14. The chapters were chopped up in various configurations to fit the page count of individual issues which led to unfortunate surgical events such as the splash page above being the last page of one issue, and the story continuing in the next issue without the splash page.
To the best of my knowledge, the first time Kingdom On An Island Of The Apes was published in full in a single issue was in this issue. Presumably it has been collected since, but I haven't come across a record of it in the GCD.
The non-comics content in this issue are as follows:
Knowing Your Place On The Planet Of The Apes! is incomplete in this issue. Two of the pages are printed out of sequence as standalone images, whilst two others are omitted altogether.
The non-comics content accounted for almost half the pages in this issue. The reprinting of a previously published story and the collation of a mass of previously unused non-comics material suggests the inventory of new material was well and truly exhausted.
This issue contains no issue number, no comics-related in-house advertising or competition or letter column. The only advertising is for pop music magazines on the inner and rear covers.
Thanks to Mark Muller for advice re: the 125% bromide note.
Update 28/1/2019: In the original post I designated this issue #NN[19]. Given the new information to hand re:
the post-August 1976 period I have now amended the issue number to #NN[18].