The agency says species ranging from a rare beach-dwelling plant in Yellowstone National Park to a caddisfly in Nebraska may warrant protection under the Endangered Species Act, but in-depth studies are needed first.
Twenty plants, six snails, two insects and a fish are on the list.
The decision comes after the environmental group WildEarth Guardians sought protections for more than 200 species.
In February, the agency turned down protections for 165 plants and animals and delayed a decision on the remaining 38.
The 29 that federal officials now say may need protection include the Yellowstone sand verbena, several species of milkvetch in Wyoming, Utah and Colorado, and a Midwestern mollusk called the Frigid ambersnail.