資料來源 : Webster's Revised Unabridged Dictionary (1913)

Ammonitoidea \Am*mon`i*toid"e*a\, n. pl. [NL., fr. Ammonite +
   -oid.] (Zo["o]l.)
   An extensive group of fossil cephalopods often very abundant
   in Mesozoic rocks. See {Ammonite}.