They do look very similar.. I think the spotting around the edge of the disc and especially on the top of the tail is different.. Also the eye structure, but it might be the angle of the pics..
I would just imagine that if the first ray I posted WAS a Castexi, that it would have been easily distinguished by the 'experts' who wrote the book.. I could be very wrong.
I just want to get to the bottom of 'P. Signata' and see if I can find some solid reference photos..