This odd critter is classified among an obscure group of cryptids known as "atmospheric beasts". These are beings that supposedly live high up in the atmosphere, within or above the clouds. They come in many different forms-- jellyfish, ribbons, giant amoebae. Some cryptozoologists even speculate that UFOs, rather than being spacecraft from other worlds, might actually be bizarre airborne life forms that either evolved here on Earth or migrated to our planet from elsewhere.
Sometimes when a meteor strikes Earth, it will be accompanied by an odd, slimy blob of tissue called "star jelly" which some believe may be the remains of atmospheric beasts struck by the falling stone. There are cases, though, where the supposed star jelly turned out to be a colony of a perfectly natural terrestrial cyanobacteria called Nostoc or one of the many varieties of slime molds (colonial organisms which are fascinating in their own right).
On an interesting side note, Sir Arthur Conan Doyle, creator of Sherlock Holmes, wrote a short story, "The Horror of the Heights", which describes an aviators encounters with "air jungles" full of weird, translucent airborne monsters.
You can read the full story here
Anyway, about this Crawfordsville Monster. In the early morning of September 5th, 1891, two ice delivery men, Marshal McIntyre and Bill Gray saw a bizarre creature diving and curling through the sky. The Crawfordsville Journal later described it as:
about eighteen feet long and eight feet wide and moved rapidly through the air by means of several pairs of side fins. . . . It was pure white and had no definite shape or form, resembling somewhat a great white shroud fitted with propelling fins. There was no tail or head visible but there was one great flaming eye, and a sort of a wheezing plaintive sound was emitted from a mouth which was invisible. It flapped like a flag in the winds as it came on and frequently gave a great squirm as though suffering unutterable agony."
The creature was later seen by pastor G.W. Switzer, whose description was similar to the Journal's report.
Eventually, the nature of the monster was discovered when two witnesses, John Hornbeck and Abe Hernley followed it and discovered that it was..... nothing but a huge flock of kildeer. Apparently the shape of the massive cloud of birds that been misinterpreted due to the dim lighting and the fogginess of the early morning.
Like a lot of cryptids, the Crawfordsville Monster turned out to be a perfectly normal, known phenomenon distorted by human perception. But even so, it still makes a pretty sweet creature.
For my interpretation, I wanted the body to have a bloby, amorphous quality like other atmospheric beasts, so I drew it with little wisps of goo trailing off it. I tried to show its fins moving in a synchronized wave like the lateral limbs of an anomalocarid.