The caption reads: "The War in America: Assault on Fort Wagner, Charleston Harbour, on the Night of July 18—The Rush of the garrison to the Parapet. From a Sketch by Our Special Artist."
This was the dreadful assault made famous in our time by the 1989 film, "Glory." Although this engraving includes some iconic features in the evolving representation of the event such as the advance of the figure with the Union flag (cf., with variations, the lithographs by Currier and Ives  or Kurz and Allison ), it offers no indication that volunteers of the Mass. 54th—or, indeed, any African-American troops—took part.
The accompanying text on p. 317 (perhaps because written by reporters "embedded"—as we would nowadays say— on the Confederate side) speaks of the battle only in more general terms:
A Blockade-runner has brought us some sketches from our Special Artist in Charleston, two of which are engraved in the present Number. Respecting the Engraving on our first page--"The Assault on Fort Wagner on the night of July 18"—our Special Artist and Correspondent writes as follows:—"I returned from the south-west just in time to witness this most formidable of all attempts made by the enemy on the defences of Charleston. You are already doubtless aware that the Federals succeeded a fortnight since in effecting a lodgment of their forces on the islands forming the approaches to the city. A temporary success enabled them to throw up works in front of Fort Wagner, and to commence an advance on the last-named stronghold. In conjunction with their iron fleet, which took up an enfilading position seawards, they maintained a heavy fire of mortars.
Further reading on this site
• Mass 54th
• West Cemetery
• African-American Amherst