7, 9, 11, to 15 and 20), often termed the king-crab, which occurs on the American coast of the Atlantic Ocean, but not on its eastern coasts, and on the Asiatic coast of the Pacific. The Atlantic species (L.
Owen, Richard, " Anatomy of the King-Crab," Trans.
The compound eye of the king-crab (Limulus) is the only recognized instance of ommatidia in their simplest state.
Polyphemus) is common on the coasts of the United States, and is known as the king-crab or horse-shoe crab.
However different in structure Trilobites may be, they all agree in possessing a head-shield usually semi-circular in shape, which results from the fusion of apparently five segments, and bears, except in some blind forms, a pair of large reniform compound eyes like those of the king-crab (Xiphosura).