If y'all are talking about the tall fellow with the BAR belt, it's hard to tell on this pic, but in a clearer one (I'm looking in "From Makin to Bougainville: Marine Raiders in the Pacific War" on page 37 if anyone has it) all you can really see is what's above his hand and it looks like a garand. I don't have my original copy of that photo here but will get it soon and maybe will be able to get a glass on it and tell.
Googled it and found a link to a better pic that can actually be enlarged (click on the pic in the link twice) with good resolution. It's clearly a garand.
File:US Marine Raiders on Cape Totkina on Bougainville.jpg - Wikimedia Commons