Cowries are a type mollusc used in a location name, Cowrie Beach.
There are a number of shelled molluscs that occur in the Family Cypraeidae, or true Cowries. These occur in tropical marine waters along the equator around the globe. However, in Britain, species of the Family Triviidae, Genus Trivia are also called cowries and look very similar to true cowries. As the author, Cressida Cowell, is from Britain, these are most likely the cowries referred to in the Books. Two species occur in the British Isles, as well as into Scandinavia: Trivia monacha and Trivia arctica.
Both species of Trivia cowries have very small, lemon-shaped shells with a flattened underside. The underside has a small oblong aperture through which the mollusk itself feeds, moves, and defecates. Both species' shells are ribbed, T. arctica is white, while T. monacha ranges from off white to a pinkish-brown with darker patches. Both species prey on sea squirts.
In the How to Train Your Dragon Book Series, the cowrie is used in a place name.
In reality, true cowries have been used for millennia as a type of money and for decoration such as in jewelry. Some types made their way to Viking Age Scandinavia through Viking trade routes. The Trivia species have been used in jewelry as beads by ancient peoples.
Cowrie Beach appears on maps in this Book as a location on the Isle of Berk. Presumably the name comes from the presence of cowrie shells.
|“||He [Hiccup] gradually became aware that what had woken him was a very faint and tiny singing noise, a reedy little sound like the wind caught in a cowrie shell, but with an edge of menace to it.||”|
|— Book 3|