Dave Thompson sent me a scan of this cancel months ago, and I never posted it because neither of us were sure at the time what Str Chickasaw meant. During the intervening period, Dave figured it out, and we now know this stamp was cancelled by the Steamboat Chickasaw, a riverboat on the Mississippi that varied its area of operations over time. In a photo below the boat was described as working rivers around Memphis in the early 1880s.
The annual report page at the bottom of this post clearly shows the boat operating in Louisiana near New Orleans with a home port of Brashear by the late 1890s. Funny how management showed the boat to lose $407 dollars in 1899 following receipts of more than $70,000. Good old fashioned Louisiana book-keeping!
Enhanced Chickasaw cancel from the stamp above