Gulf of Mexico Conch shells. These come out of Haiti and Mexico. Approx 8"-10" in length. These are "slits" so they will have a cut in the shell near the "spire" or "cone" that was done in order to remove the animal for food consumption.
Please note that there is no such thing as a "perfect shell". Shells have imperfections, chips, scrapes, and bumps that all add character to the individual items. If they were perfect than they wouldn't be real.