Gymnocalycium horstii var. buenekeri is from Brazil, has harmless spines going against the body of the plant and only 4-5 ribs. Gymnocalycium eurypleurum is from the border of Paraguay (Cerro Leon) with Bolivia and is a relative of the anisitsii/damsii group. Search the name on the internet and you will see that this plant is indeed Eurypleurum. I have both Eurypleurum and horstii var. buenekeri and they do not even look similar. Eurypleurum is quite an interesting and rare plant in collections and it does very rarely offset, while horstii is bigger, getting to 20-25 cm and offsets after some time. Eurypleurum has quite long spines, straight and stout (not curved on the body, like in the case of horstii) under a good sun exposure and will get to 7-10, maybe 15 cm across.
