According to the box, they're Fijne Speelkaarten whist type no. 215. According to the seller, they were manufactured by Brepols circa 1925. The World Web Playing Cards Museum partially backs this up, identifying them as part of the Royal Cards series ("WWPCM04416/03C: variant with dutch aces"). The Royal Cards series 3 was introduced in 1916, but was in print for decades; these ones are in monochrome, rather than colour, which suggests an earlier date. 1925 is a reasonable guess.
They're the standard Dutch pattern for cards (which is actually Belgian); this may explain why they only cost me £3.49. I'm a sucker for illustrated aces, though, so went for it. The prettiest one in this pack (the only one that has canals on it) is for the Aces of Spades, which is why I scanned it upside-down for your critical appraisal.
Interestingly, the box opens from the side rather than from the top. Well, interestingly for me, anyway...