Wallace might have been part of the publication, but he had a completely different view to what scientist accepts today. Also, his obscurity could be as regards to the fact that Wallace had never intended his work to be published at that time.
I could say this is the problem. In science, when we want to reference the author in the middle of an article, we forget the second person. Only the first author rings bell.
Thanks so much for that apt comment. Yes, authorship is often reserved for the name cited first. However, I believe Wallace's claim to credit is not based on the authorship of this paper. It is based on the considerable work he did independently in identifying and categorizing species. (See, for example, the Wallace Line.) He seems to have been quite prolific and insightful in that regard. Of course, I only just learned about him so I am hardly an authority.