First of all, we should note that this term can be considered offensive and can only be used in physical anthropology.
There are a number of traits that are said to typify negroid people. Among them are such things as femurs that are straighter than those of other races as well as flaring nasal openings in the skull. They also lack a "nasal sill." Negroids are also said to have jaws that protrude more than those of other races (this is called prognathism). They have more rectangular eye orbits and larger teeth.