Eurypteroidea \Eu*ryp`te*roi"de*a\, n. pl. [NL. See Eurypteroid.]

(Paleont.) An extinct order of Merostomata, of which the genus Eurypterus is the type. They are found only in Paleozoic rocks. [Written also Eurypterida.]

Source: Webster's Revised Unabridged Dictionary (1913)