Here we have the "Sea Fan" Coral, which the card tells us is "the beautiful skeleton of a colony of marine animals". We also learn from the text that it is in the same family, anthozoa, as the Sea-Anemones, this one being Anthozoa Gorgonia, one of the sea-whip corals, and quite soft to the touch. The text tells us that it "...is quite common off the British coasts, where it is found in 10-25 fathoms of water."
I could not find another of these anywhere on cards, but I have now been told that card 25/48 of Brooke Bond Canada`s "Exploring the Ocean - Explorons L`Ocean" (issued in 1971) shows a selection of corals, including elk horn, sea whip, stinging coral, gorgonia, star coral and brain coral.
Although it does not show our coral, instead picking to showcase a more utilitarian, pipe-like coral, of the Madrepore sort, card 14/25 of W.A. & A.C. Churchman`s "Nature`s Architects" tells us a lot more about corals, including that they "...are of four main classes; the branching corals ... and the massive corals, both of which types play such an important part in the formation of coral reefs ; single corals, and the familiar red coral used as beads, etc. These beautiful objects are really "skeletons" formed by the coral-polyps from carbonate of lime, extracted from the sea water, the pitted appearance of the type illustrated being due to the mouths of the numerous cells in which the coral polyps formerly lived."
The same Madrepore coral appears on another card by W.D. & H.O. Wills, namely No.15 of "Do You Know" second series, issued in 1924 - this card telling of how the coral reef is formed - as well as on Ching`s "Do You Know", card No.11, again "How coral is formed", issued in 1962. That last one was also issued as a trade card, by Tonibell ice cream, but a year later in 1963.
That is all I have been able to track down so far.
We first encounter our set in part IV of our original Wills reference booklets, where it is described as :
349. 50 WONDERS OF THE SEA. Fronts printed by letterpress in colour. Backs in grey, with descriptive text. Issued 1928.
A. Home issue. Wills` name and I.T.C. Clause at base of back.
B. General Overseas issue. Anonymous backs. Two grades of board, (a) white (b) cream.
In both our World Tobacco Issues Indexes, the text has reduced to simply :
WONDERS OF THE SEA. Sm. Nd. (50). See W/349.A
However the anonymous version is stoved off to the back of the book, coded as ZB07-905 in the updated version, and ZB6-83 in the original.