Psorophora ciliata, Fabr., is the only species of the genus Psorophora known to occur in the United States. It is a widespread species and is known to the writer to occur in Massachusetts, New Jersey, Pennsylvania, District of Columbia, Vilginia, Kentucky, Illinois, Florida, Louisiana, Arkansas, Nebraska, Texas and California. It is, however, rare in its northern range and seems to be a lower austral form. It may have a tropical range, but among many mosquitoes received by the writer during the past year from Mexico, Nicaragua and Cuba, this species does not occur. In his “Notes on the Mosquitoes of the United States” (Bulletin 25, New Series, Division of Entomology, U. S. Department of Agriculture), published August 23rd, 1900, the writer calls attention to the fact that Psorophora and Megarhinus have not been studied by investigators engaged in working upon the transfer of Haematamoebæ by mosquitoes, and urges that physicians and bacteriologists in our Southern States pay some attention to the mosquitoes of these genera.