Ὑλαίην: cf. 18. 1 n. The ‘grotto’ is part of the legendary furniture of the Echidna story; cf. Hes. Theog. 297.
διατεινόμενον. The Scyths drew to the shoulder, not to the breast (like the Cretans); they used both hands indiscriminately (Plat. Laws, 795 A). For Heracles' Scythian bow cf. Theoc. xiii. 56.