Studies of new finds of omomyid primates from the lower Eocene Willwood Formation of northwest Wyoming reveal the presence of a new genus and two new species of anaptomorphines and a new species of omomyine. All were apparently short-lived immigrants into the Bighorn Basin. The new genus and speciesTatmanius szalayi is typified by a diminutive single-rooted p3 and a bilobed-rooted p4 with a crown smaller than ml. These traits were probably derived fromPseudotetonius and parallel similar conditions inTrogolemur andNannopithex. The new speciesArapahovius advena is the first occurrence ofArapahovius outside the Washakie Basin, where it appears to have also been a vagrant species.Steinius annectens, sp. nov., is larger than the olderSteinius vespertinus and strengthens the alliance between this genus and BridgerianOraorays carteri, although which species ofSteinius is closer toOmomys is not yet clear. The available evidence suggests a derivation ofOmomys (Omomyini) fromSteinius and all Washakiini from the anaptomorphineTeilhardina, which would indicate that Omomyinae were at least diphyletic. Preliminary evidence suggests that the geographic distributions of at least some Willwood omomyids correlate with paleosol distributions.