Busycon odontophore protractor muscles were examined by conventional force recording and by the single and double sucrose-gap voltage clamp technique. The mean compound resting membrane potential was -61.3 mV and the muscles showed considerable mechanical summation in response to direct electrical stimulation. 2. Responses to high K+ salines consisted of a maintained dose-dependent depolarization upon which were superimposed spike-like action potentials of 3-9 mV each of which generated a fast twitch contraction