The "Kidney" is Northwest Reef. Its a couple miles northwest of North Bass Isl and West Reef. Some GPS units show the reef which is shaped like a kidney and some only show and "R". Only a slight structure change but it covers a large area just smaller than a square mile. North # is 44.5 and west # is 58.3. Its on the Hot Spot charts you can buy at bait shops with these same numbers.