Anyway, Asia isn't the only continent with giant softshells. There are also giant African species (or one anyway: the African softshell Trionyx triunguis), and in an October 2009 post on the SA Reptiles discussion board, forum-user Herphabitat posted several photos of a huge, dead softshell he and colleagues discovered on a peninsula in the mouth of the Congo River. From a distance, they first assumed that the carcass was that of a dead sea turtle (perhaps a Leatherback Dermochelys coriacea). On discovering that it was a softshell, they assumed that it had died further up-river and had then been washed down to the edge of the Atlantic. However, this assumption isn't warranted, as T. triunguis inhabits brackish waters in places, and has even been captured 3 or 4 km out at sea (this was close to the mouth of the Gaboon River: Ernst & Barbour 1989). T. triunguis is a widespread softshell, occurring from coastal Turkey, Israel, Lebanon and Syria all the way west to the Atlantic coast of the Congo region.
While we're here... it's been suggested that there might be monster examples of T. triunguis whose lengths well exceed 1 m. In his 1987 book on the mokele-mbembe, Roy Mackal wrote about the 'Ndendeki', a giant turtle of Lake Tele (and perhaps the surrounds) in the Congo. Local people didn't know much about it - other than that it was a turtle and that it was very large - but an estimated diameter of a ridiculous 4 or 5 m was suggested (Mackal 1987, p. 267). Mackal and his colleague Marcellin Agnagna both assumed that exaggeration had occurred, and that a more reasonable size might be about 2 m (this is for length [of the softshell carapace] and not diameter). That's still pretty incredible - though certainly not impossible - and really needs verification [adjacent Ndendeki reconstruction from Mackal (1987, p. 271)].
Anyway, full credit to Herphabitat for his excellent photos. Please visit the SA Reptiles post to see more images and more information. Thanks to Markus Bühler for bringing this to my attention.
"The boney part of the the carapace measured a CCL of 55cm and CCW of 54cm. The total length of the soft shell was CCL: 106cm"