We examined the toxicity of Venerupis semidecussata, which caused a poisoning case at Toyohashi City in July 1948, and found the paralytic poison of toxicities varying from 3.3 to 45.7mg. or from I to 15 M. U. per g. liver. The distribution of poisonous Venerupis was confirmed to be limited to the narrow area of the Yagyu-River.