Reading further in Scholem, I just came upon that miraculous word belimah. Here is what Scholem says about it.

Various peculiarities of the terminology employed in [Sefer Yetzirah], including some curious neologisms which find no natural explanation in Hebrew phraseology, suggest a paraphrase of Greek terms, but most of the details still await a full clarification. The precise meaning of the phrase Sefirot belimah which the author constantly uses and which may be the key to the understanding of what he actually had in mind when speaking of the Sefirot, is a matter of speculation. The second word belimah which may be taken to denote or to qualify the specific nature of these “numbers” has been explained or translated in accordance with the theories of the several writers or translators: infinite Sefirot, or closed, abstract, ineffable, absolute Sefirot, or even Sefirot out-of-nothing. If the author of the book wanted to be obscure, he certainly succeeded beyond his wishes.