Ornithocheirus is a genus, not specific species of Pterosaur, however the taxonomy has caused many headaches for researchers and it is unclear as to how many species it represents. The Genus was first discovered in 1861 in England. Since then other species (likely representatives with variation such as local variants and not all true species) have been found and documented.
Between 1869-1870 the young researcher Harry Grovier Seeley was charged by the Sedgwick Museum in Cambridge to bring order to the Pterosaur fossil collection. He eventually listed 28 species in the Genus Ornithocheirus which means "Bird hand". This is because during this time he and some others believed that the wings of these pterosaurs represented a stage in Evolution towards the development of the Bird hand. When Seeley published his conclusions in his 1870 book Ornihtosauria, it prompted Richard Owen, the founder of Dinosaur paleontology, to reject the naming since Owen was a Creationist and not an Evolutionist, and therefore felt that the name giving homage to the theory of Evolution was inappropriate. Since the 1970's most fossil remains have been found in Brazil and most have been much better quality than the ones found in England.
It is estimated that the largest species of Ornithocheirus approached a wingspan of 33 feet, give or take, making some the size of a small airplane, while other specimens had a wingspan of only 8 feet. Most specimens seem to have topped out at 20 feet however, leading to some confusion and speculation over the potential size of Ornithocheirus pterosaurs. What may be the most telltale feature of these animals is it's "spoon bill". Studies have shown that Ornithocheirus had very sharp senses and that it would have been a remarkable hunter.
Incidentally, there have been reports of pterosaurs, some identically resembling Ornithocheirus, from South America within the last 100 years, by people that have had nothing to do with fossil excavation. Are these stories hoaxes or are there some Pterosaurs left? Only investigation will tell.