I have seen the Turtle Shell used on a variety of Medicine bags and Sacred Items, but seldon on a daily-use
possibles bag. Never let it be said, however that it is inappropriate! Just that the shell might not hold up to rough use.
Well, I'll say it. In about 30 years of visiting museums to examine shot pouches, shooting bags, hunting bags, etc, plus getting into some of the better private collections, I've had my hands on literally thousands of original bags with a history of use in the trans-Mississippi west prior to 1900. I've seen thousands more. I've read historical descriptions of bags, and ethnographic descriptions of bags. But I've never run across mention, or an example, of a bag made from a turtle or tortoise shell.
I've seen shells used as boxes, shells in medicine bundles, shells as ornaments, shells that were kept for who-knows-what-reason, but no bags. Until someone can point to an actual example or historical mention, I'm going to regard anyone carrying one as farby, as a pork-eater, or as a re-enactor of 1950s Friendship Indiana shooting matches. (Ah the days when "If they'da had it, theyda used it" was king. . . . But they
DID have "it", and they
DIDN'T use it that way.)
From the pic it does look like a nice piece of work. I've never understood putting the effort and expense into doing something like that rather than something that is historically accurate.