Key-hole limpet or Key-hole saw

(Zool.), a gastropodous mollusk of the genus Fissurella, so called from having in the summit of the shell an oval fissure constricted in the middle so as to resemble a key-hole. Baird. — Key-hole saw, a narrow and slender saw, by means of which pieces with curved outlines may be formed by sawing; a compass-saw.