This is a very strange book. The 'True Story' of the varied crypto-creatures covered in this book is - largely I think in Mark Hall's view rather than the two other contributors - that they are scale-and-tail, fully evolved real animals. And not just animals, but primates, in fact our sea-going cousins.
Hall's candidate for the origin of this hitherto-unknown extension of the Order 'Primates' is the Oreopithecus bambolii, most fossil remnants of which have been found in the Tuscan region of Italy. What makes Hall suggest that Oreopithecus is the ancestor of an entire universe of semi-human sea creatures is the curious formation of its feet, with a big-toe at right angles to the other four. In one great leap of palaeozoological derring-do, he hypothesises that “the tripod like foot of this primate may have developed into the four-toed foot of the North American freshwater apeman.”
Hall takes every every folktale, legend, campfire story or traveller's tale and spooky encounter in the swamps and presents it as a first-hand account of 'scale and tail' aquatic hominids. They seem to come in a great variety shapes and sizes to cover any possible alleged contact account, a bit like UFO aliens, until they all got whittled down to the standard Streiber format.
Sometimes the reported creatures do not fit into even the broadest depiction of an aquatic primate. Hall quotes case from Spain in 1739 when a creature with a tapered head, hairy back and short arms but with very elongated fingers was caught in a fishing-net. Its heels had fins “resembling the winged feet with which the painters represent Mercury”, and a twelve inch dorsal fin. Very un-apelike. But Hall has an answer, the merman is wearing a hydro-dynamically designed suit for speed and manoeuvrability - “this suggests that Homo sapiens were not the only primates learning how to use tools.”
In 1565 a traveller in the Holy Land discovered a 'mermaids skin' in a local market. It consisted of a torso with a fish tail, from the navel up the creature was human, but the head and arms were missing. A part decomposed dugong or other sirenia? No, to Hall the missing head and arms suggest that it was “a water ape's discarded protective gear.”
Almost any report can be shoehorned into an explanation involving aquatic apes. In Australia, Aboriginal people have accounts of merpeople, who sometimes appear to have a fish-like tail and on other occasions are able to walk on dry land. The answer: “These accounts tell us something we have suspected all along in our research. The fish-tail is detachable”. Perhaps, Hall suggests “the fishtail has become less essential for survival and may be more of an aesthetic choice.”
It is remarkable the range of creatures that Hall has corralled into his merfolk menagerie, from the Lizardmen of the Carolinas, to the man-monkey of the Shropshire Union Canal. Any mysterious or folkloric figure vaguely associated with a water feature – and even some from desert regions - can be explained as an aquatic ape. West Virginia's 'Mothman' even gets recruited to the ranks.
But of course there is not the slightest trace of any actual physical evidence, as we former ufologists like to call it. This huge, world-wide population of sea-going primates, and quite a few inland ones, seems to have lived alongside us for millennia without anyone coming across a body or even a discarded 'aesthetic' tail, other than a vague story about a Levantine market five hundred years ago.
So is this a crank book espousing a crank theory? Well I have to say yes. It reminds me more than anything of the 'crypto-terrestrials' promoted by Mac Tonnies, a ufologist who believed in the existence of a race of intelligent quasi-human 'ultraterrestrials' which also had lived on earth alongside us for millennia. Just like the merfolk, the race who were allegedly responsible for the entire UFO phenomenon seemed to manage this without leaving any tangible trace of their existence. 
Unlike Tonnies' very vague account of the nature of the cryptoterrestrials, Mark Hall presents us with a wealth of detail, and the greater part of the text is re-telling and transcriptions of hundreds of accounts of strange sightings as 'memorates'. They come from ancient texts, early modern chronicles, nineteenth century accounts of explorers and anthropologists, from modern newspapers, and of course from the stories collected by folklorists, and they are all meticulously referenced after each chapter.
If you can ignore its blindness to the entire world of folklore studies displayed here, there is a lot of interest in the raw data of the individual stories. But it is frustrating being bogged down by the speculative commentary on the accounts, and i am trying hard not to shout things like “but that's what boggarts do as well” (jumping on passing vehicles), “there are no aquatic giant ape-men in Shropshire”, or asking why the Kelly-Hopkinsville 'goblins' are drafted into the theory, but not the much more mer-creature like Pascagoula aliens.
With a wider perspective this could have been a worthwhile book, but it is ruined by the obsessive focus on an evidence-free theory which refuses to accept that the true realm of merpeople, ultraterrestrials and the hundred other cryptids that haunt our planets is the human imagination.
- John Rimmer