[1] Of these two nominative singular forms, the one proffered as an alternative here, skni/y, is actually the normal form: sigma 640. The headword form itself, ski/y, is attested only in lexicography and grammars; cf. ps.-Herodian, Epimerismi 127.5-6 (where skni/y is identified as a bird or an animalcule), Hesychius sigma1398 (where ski/y is identified as the name of a bird), Hesychius sigma1046 (where skni/y is identified as 'a pale tetragonal animal').
[2] Presumably extracted from somewhere; probably the much-quoted Psalm 104.31 LXX (see at sigma 640).