Science magazines
- Spruce-fir Moss Spider
- Squirrel Chimney Cave Shrimp
- St. Andrew Beach Mouse
- St. Croix Ground Lizard
- St. Thomas Prickly-Ash
- Star Cactus
- Steamboat Buckwheat
- Stebbins' Morning-glory
- Steelhead Trout
- Steller's Eider
- Steller's Sea Lion
- Stenogyne Bifida
- Stenogyne Campanulata
- Stenogyne Kanehoana
- Stephens' Kangaroo Rat
- Stirrupshell
- Stock Island Tree Snail
- Suisun Thistle
- Swamp Pink
- Tampico Pearlymussel