494 PROCEEDINGS OF THE NATIONAL MUSEUM vol. iie 



Head slightly wider than the thorax; black except entu*e face, small 

 spot back of compound eye, base of mandible, and patch on the scape, 

 all of which are cream colored; clypeal margin with three low denticles, 

 the medial one sometimes slightly divided, all usually low and often 

 indistinct; clypeal surface slightly convex; mandibles with a rounded 

 extension medially on the lower margin; antennae with the apical 

 segment slightly curved. 



Thorax black except for two elongate, widely separated patches on 

 the pronotum, the metanotum, and the tegulae, all of which are cream 

 colored; tegulae low and smooth; enclosure lightly ridged longitudinally 

 but somewhat u-regular; mesosternal tubercles absent; legs with the 

 first two pair largely yellow except dark patches on the dorsal sides of 

 the femora; the hindlegs yellow except the apical half of the femora, a 

 patch on the apical end of the tibiae, and small patches on the tarsi, all 

 of which are dark amber; wings sub hyaline with the stigma light. 



Abdomen black except for two separated patches on tergmn 1, 

 narrow bands on terga 3 to 6, divided bands on sternites 2, 3, and 4, all 

 of which are cream colored; pygidium with the sides subparallel and 

 the apical end truncate. 



C. nigrescens nigrescens F. Smith is close to the following species in 

 general appearance: astarte Banks and dentifrons Cresson in the East- 

 ern States. In the West it is near C. aegualis Provancher. The 

 form of the clypeal process and the pygidium usually will separate 

 them. The cream-colored markmgs of the nominate subspecies also 

 will aid in its recognition. In the Pacific Coast States the cream- 

 colored markings gradually are replaced with yellow. Mating pairs 

 may be found in southern Oregon, where one sex has yellow markings 

 and one, cream-colored markings. Some individuals show varying 

 amounts of cream and yellow. In California C. nigrescens munda 

 Mickel, the yellow form, predominates. 



Type. — The type female of C. nigrescens F. Smith, from Nova 

 Scotia, is in the British Museum, no. 21.1,431. 



Distribution. — This is the most widely distributed species of 

 Cerceris in North America. It ranges from New England west 

 through the Northern States to the Pacific Coast and south to Nevada, 

 Utah, Colorado, Nebraska, Iowa, Illinois, Ohio, and North Carolina. 

 It is recorded also from Alaska. As indicated above, the subspecies 

 munda Mickel largely takes over in California. 



Prey record. — Hyperodes solutus (Boheman) (New York), H. 

 delumbis Gyllenhal (Krombein, 1936, 1938, New York), Sitona 

 hispidulus (Fabricius) (Krombein, 1936, 1938, New York), Gymnetron 

 antirrhini PaykuU (Krombein, 1938, New York). 



Plant record. — Achillea sp. (CalifoiTiia, Idaho, New York, 

 Oregon), A. millefolium (Wyoming), alfalfa (Alberta, Idaho, Oregon), 



