A first account of the habits of Pseudomasaris vespoides has been given by Dr. A. Davidson ('13). He found their nests, usually attached to a twig of a low bush, and built after the manner of the mud dauber wasp but of stony hardness. The completed cell was closed by a stopper of clay which was depressed in the center so that the top of the nest presented a series of small cups. The cup was believed to conserve the rain, soften the stopper and enable the insect to more easily emerge. The cells were thought to have been stored with small larvae. According to Bradley ('22), P. vespoides is found in South Dakota, Idaho, Colorado, New Mexico, Utah, Nevada and California.