This is very preliminary, but it seems that Atakapa refers to a groups of
tribes related linguistically that generally lived in the lower Mississippi
valley. Studies of the languages were done by Albert Samuel Gatschet and
John Reed Swanton. One of the Karankawa groups (coastal Texas) was/is some-
times thought to be Atakapan, but that is tenuous. That group is the Hans,
who shared Galveston Island with the Capoques. Cabeza de Vaca thought that
they may have been Akokisas, and Atakapan group, but many don't buy into that.
I'll see what else I can find, but now you have a region, some names, and
some linguists. Plus whatever anyone else sends in. Good luck!
S.I.S.S.