If she sells seashells on the seashore, Instagram’s nail artists are keen collectors because my feed is awash with hyper-realistic scallop shell designs just in time for summer. What are seashell nails and how do you achieve them?  If Instagram is anything to go by, the shell of choice for nails is the humble scallop — though the designs are anything but basic. Take Kalala’s viral set by Mani Concept , which pairs a milky base with brown ridges to mimic the natural nuances of a real shell, finished with soft white contours for shape and a pearl-like gem at the cuticle for good measure.   Advertisement ADVERTISEMENT Nail artists like Annabel Maginnis are going even further with 3D gels, creating raised contours reminiscent of a scallop shell, and when layered over neutral ridges, they’re unmistakably beachy.  Natalia Mercedes , a nail artist and founder of Sad Girl Nails Studio in New York City, is especially a fan of this maritime-inspired design.…