This the only such bottle I've found in Florida. I've always thought of it as American-made. Rex Wilson (BOTTLES ON THE WESTERN FRONTIER) illustrates a number of "beer bottles, export style" which are close. These would be for 1870s lager beer. I'm eager to see your Texas finds, nhpharm, especially any with the raised ring around the mold vent nipple.
I lugged home almost 150 British blackglass bottles from my most recent dig...will take a look and see if any of them have this base. I think most of the ones I dug this trip are a little too early. I would say that I believe the bottle you have posted is British. The 1870's lager beer bottles from the US that I have seen are typically similar in form but are amber and typically have the initials (such as C&I) embossed on the base.