How can you tell a dog whelk from a periwinkle?

Dog whelks and periwinkles can be distinguished by their shell shapes and features. Dog whelks usually have elongated, conical shells with a more pronounced spiral pattern and a pointed apex, while periwinkles possess a more rounded, dome-shaped shell with a smooth texture and a flattened top. Additionally, dog whelks often have a larger and more robust shell compared to the smaller, more delicate periwinkle. Observing these characteristics can help identify each species accurately.