A variety of penny red that does not seem to have been listed in the Stanley Gibbons specialised volume 1, is that of the long and short perforations found on some of the stamps printed from the "A" and occasionally the "T" rows of the sheet.
Some of these varieties are quite scarce, and consequently I only have one example of which to show you.
With reference to these perforation varieties I could not but notice the lack of information relating to the almost 'Square' stamps that can be found with the 1854 penny red, unlike the normal versions with 16 perforations horizontal and 19 perforations vertical, these particular ones have 16 horizontal but only 17 vertical perfs.
It would appear that the normal stamp " on cover/entire " is given a listing, but with this poor little Cinderella who's a bit 'Square' to say the least doesn't even get a mention, having a stamp that is a completely different shape from the rest of the sheet does not seem to have interested specialised catalogues relating to this particular variety, as in the past it has only been treated as a novelty.
In 1854 when these perforated stamps were first issued, perforating machines were still in their infancy with their introduction being made by Irish born Henry Archer (1799-1863) and his invention for separating postage stamps, he later sold the rights and patents of his invention to the government after successful trials of the Prince consort essay of 1851 at a later date.
Here is an example of such a stamp on cover when comparing it with the normal version. >

This type of perforation variety is worth looking out for. WM.