Ammonite
a large genus of fossil chambered shells, belonging to the class cephalopoda, the order tetrabranchiata, and the family ammonitidæ. The shell is discoidal, the inner whorls more or less concealed, the septa undulated, the sutures lobed and foliated, and the siphuncle dorsal. ranging The ancients venerated them, as the Hindus still do. About 700 so-called species have been described, rang from the trias to the chalk.