Thanks very much for the advice everyone. I did not consider the dangers of preservation of these old prints. There is print-shop near me so I will take them in and see if I can sort out some acid-free matting.
Here's three more old prints for you to enjoy. These are in a wonderful old volume called 'Mysteries of the Universe vol.1' (intro. by Lord Avebury and with essays by 'leading specialists') I own that was published in about 1930. It is a somewhat weird book as it is completely without structure. There are over a couple of hundred short journalistic-style essays on the subjects of "The Heavens, The Earth, Plant Life, Animal Life and The Mighty Deep' but they are written in a totally random order. You have, for example, an article on 'The Giant Reptile of Wyoming' followed by 'Mars as a Home for Men' followed by 'St Elmo's Fire' and 'The Honey Bee'. It's impossible to find anything in the book.
My favourite illustrations are one of a deep-water Japanese spider-crab that is depicted by the illustrator as walking along a sandy beach

, and a depiction of the surface of Mars showing canals and buildings!
Anyway, here are three typical illustrations showing a somewhat gelatinous giant squid being attacked by a sperm whale (with a small human skeleton for no apparant reason on the sea bed), squid squirting ink at a conger eel and some amorphous octopi.
Well I liked them anyway!