78 AMERICAN HYMENOPTERA. 



Fourth dorsal segment entirely black and the fifth mostly so. 



nigrodorsalis. 



Basal portion of fourth dorsal abdominal segment bearing yellow 



pile sulfnratiis. 



22. Scutellum and first dorsal abdominal segment yellow 23. 



Scutellum and first dorsal abdominal segment entirely or mostly 



black crotcliii. 



23. All the dorsal abdominal segments beyond the second clothed with 



reddish or ferruginous pile liaueri. 



The apical portion of the abdomen not so clothed 24. 



24. The two apical dorsal abdominal segments black.. ..iiiexicensis. 

 The two apical segments with white pile above. 



robiistus var. cinctns. 



25. Dorsum of abdomen entirely black iiiedius. 



Dorsum of abdomen bearing more or less yellow or white pile. ..26. 



26. The two apical dorsal abdominal segments entirely dark 33. 



One or both of the two apical dorsal segments bearing more or 



less yellow, yellowish or white pile 27. 



27. Dorsum of thorax unicolorous 28. 



Dorsum of thorax bicolored 29. 



28. Mesopleura yellow moutezimiae and weisi. 



Mesopleura black eciiadorins. 



29. The first two dorsal abdominal segments yellow 30. 



The first two dorsal segments black 32. 



30. Pleura yellow iiigrodorsalis. 



Pleura black 31. 



31. Third dorsal abdominal segment black. 



I'obustus var. steinbaclii. 

 Third dorsal segment entirely or mostly clothed with yellow pile. 



robustiis (typical). 



32. vSegment four of the abdomen yellow above and segment five 



mostly black trinominatus. 



Fourth and fifth dorsal abdominal segments both clothed with white 

 pile robustus var. hortulaiis. 



33. Fourth dorsal abdominal segment yellow 34. 



Fourth dorsal abdominal segment black 37. 



34. The first four dorsal abdominal segments clothed entirely with yel- 



low pile 35. 



Not all of the first four dorsal segments entirely clothed with yel- 

 low pile 36. 



35. Mesopleura mostly yellow fervidus. 



Mesopleura mostly black souomae. 



36. Face and occiput clothed with mostly yellow pile..vosiieseiiskii. 

 Face and occiput entirely or mostly black californieiis. 



37. The third, and only the third, dorsal abdominal segment bearing 



yellow pile 38. 



