Old star maps with unknown constellations

A recent study in the Bodel Nijenhuis Collection of maps, atlases, topographical prints and drawings in the Leiden University Library has resulted in the discovery of an enigmatic pair of celestial hemispheres of which the origin appears to be unknown.

Northern hemisphere (COLLBN Port 169 N 3a)          
Southern hemisphere (COLLBN Port 169 N 3b)

The celestial hemispheres, printed on separate sheets, were apparently removed from an early 17th-century book and pasted on a piece of cardboard.
The iconography of the depicted constellations on both hemispheres can be closely matched with those on a 34-cm celestial globe first published in 1603 by the Amsterdam cartographer-publisher Willem Jansz Blaeu (1571-1638). Amongst the many similarities that can be noted are the depiction of the constellation Argo Navis as a Dutch East Indiaman and the naming of the Plancius constellation Toucana as Lang.

Two Unknown Constellations

However, the author of this pair of celestial hemispheres did not follow Blaeu's celestial globe in every detail and made a few remarkable changes.
In the southern hemisphere, below the feet of Centaurus, the Plancius constellations of Chamaeleon, Musca and Triangulum Australe were replaced by two constellations of his own making: Ceneus (referring to the Lapith Caeneus) and Siren.
So far, I have not seen these constellations depicted on any other 17th-century star map known to me, nor have I found them mentioned in any work known to me about the history and lore of the Western constellation figures.