Merriam-Webster Collegiate Dictionary - sinistral

 adjective  Date: 1803 of, relating to, or inclined to the left: as  a. left-handed  b. of a gastropod shell having the whorls coiling counterclockwise down the spire when viewed with the apex toward the observer and having the aperture situated on the left of the axis when held with the spire uppermost and with the aperture opening toward the observer — compare dextral b