merostomata, prop. n. pl. [NL., fr. Gr. me`ros thigh + , -, mouth.].
A class of Arthropoda, allied to the Crustacea. It includes the trilobites, Eurypteroidea, and Limuloidea. All are extinct except the horseshoe crabs (Limulus) of the last group. See Limulus. [1913 Webster]