In Five Children and It the Psammead is described as having "eyes [that] were on long horns like a snail's eyes, and it could move them in and out like telescopes; it had ears like a bat's ears, and its tubby body was shaped like a spider's and covered with thick soft fur; its legs and arms were furry too, and it had hands and feet like a monkey's" and whiskers like a rat's. When it grants wishes it stretches out its eyes, holds its breath and swells alarmingly.
The five children find the Psammead in a gravel-pit, which used to be seashore. There were once many Psammeads, but the others died because they got cold and wet. It is the only one of its kind left. It is thousands of years old, and remembers pterodactyls and other ancient creatures. When the Psammeads were around they granted wishes that were then mostly for food. The wished-for objects turned into stone at sunset if they were not used that day, but this does not apply to the children's wishes because what they wish for is so much more fantastic than the wishes the Psammead granted in the past.[1] (Chapter 1)