20 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 68 



Senotainia have been largely disproved by actual observations on 

 the larvae of several species, recorded elsewhere in this paper. 



The habit of trailing or "shadowing" the host as it carries the 

 prey to its nest seems to be more highly developed in this genus 

 than in any other in the group. This habit appears related to two 

 structural characters not occuring in such a pronounced degree in 

 other North American Miltogrammini, excepting in the genus 

 PachyophtJialmvs, which are, namely, the conspicuously enlarged 

 facets of the front part of the eyes, and the uniformly narrower 

 front and larger development of the eyes in the female as compared 

 with the male. The possession of larger eyes with the enlarged 

 facets, should in all probabihty be regarded as speciahzations per- 

 mitting the female to keep herself oriented more readily with the 

 rapidly moving form of the wasp she follows, while in flight. 



So far as observed, the members of this genus display little or no 

 interest in burrows stocked with food, or the paralyzed victims of 

 the wasp, when it drops them outside its burrow, but is strongly 

 excited b}^ the presence of the wasp carrying its prey, and is seem- 

 ingly stimulated to larviposition only in the presence of this com- 

 bination. 



KEY TO NORTH AMERICAN SPECIES OF SENOTANINIA 



1. Sternopleura with one bristle 7. 



Sternopleura with two bristles 2. 



2. Abdomen red, at least on the sides; third antenna! joint red or at most with 



blackish tomentum over the red 4. 



Abdomen wholly black 3. 



3. The two frontal rows of macrochaetae, at their middle, separated by a distance 



greater than width of either parafrontal; three distinct postsutural dorso- 



central bristles trilineata Van der Wulp. 



The two frontal rows of macrochaetae, at their middle, separated by a dis- 

 tance less than width of either parafrontal; not more than two postsutural 

 dorsocentrals differentiated lito rails Allen . 



4. Second abdominal segment with median marginal bristles 6. 



Second abdominal segment without median marginal bristles 5. 



5. Arista thickened almost to the tip; third antennal joint at least nearly three 



times length of second joint rufiventris (Coquillett). 



Arista thickened on basal half; third antennal joint at most scarcely exceed- 

 ing two times length of second joint flavicornis (Townsend) . 



6. Arista thickened on the basal two-fifths; bucca in profile usually not more 



than one-twentieth the eye height; two proclinate orbital bristles; outer 

 forceps of male genitalia with a strong rounded hook, directed anteriorly. 



rubriventris Macquart. 



Arista thickened on basal three-fifths; bucca in profile at least one-tenth eye 



height; usually but one proclinate orbital bristle; outer forceps of male 



genitalia with stout, sharp tip posteriorly directed and apposed to the tip 



of the inner forceps vigilans Allen. 



7. Costa, near the humeral angle, with erect, radiating, bristly hairs; inner for- 



ceps of male genitalia broadly triangular when viewed from behind. 



setulicosta, new species. 



