44 AMERICAN HYMENOPTERA. 



areolated as described, but more frequently an intermediate 

 condition exists where the carinse are present but more or less 

 indistinct. In all parts of the range of this species there are 

 a few small specimens ; these seem to be especially numer- 

 ous in Colorado, and might at first be looked upon as a 

 separate species or subspecies, but since they agree with the 

 larger specimens in structure and color, and show the same 

 variations, I do not see how they can be considered even a 

 subspecies. O. tityri Pack, was at first proposed as a variety 

 of this species, and later raised to specific rank, the differ- 

 ences given being that tityri is " smaller, with the abdomen 

 considerably shorter, the metathorax strongly areolated, and 

 the male clasps subtriangular, obtusely rounded ; while in bi- 

 lineatus the metathorax is smooth, and the male clasps are sub- 

 triangular, obliquely truncate and acute posteriorly." After 

 a careful examination of a large series, however, I find that 

 none of these characteristics are constant. I have worked 

 upon these for some time, and do not believe tityri can be 

 given even subspecific rank. Occasionally characteristic 

 tityri specimens will be found, but there is a complete grada- 

 tion from these to the typical bilineatus, and these interme- 

 diate specimens are by far the most abundant. Dr. Felt 

 states that tityri "has a well-defined period of flight, which 

 does not overlap the time ,(9. bilineatus is abroad, except in 

 the case of scattering individuals. This species appears 

 early in May, is most abundant till the latter part of the 

 month and occasionally in July, with belated individuals to 

 October, while O. bilineatus does not occur till August, and 

 then only in scattering numbers till the latter part of the 

 month. This marked difference in the time of flight between 

 these two parasites indicates either that they represent two 

 broods of the same insect or else they are distinct species." 

 Specimens before me, however, show that characteristic 

 bilineatus are taken quite as frequently early in the summer, 

 and I have taken them at Amherst, Mass., as early as April 

 15. Many of the more slender specimens closely resemble O. 

 luteus, and some writers have considered the South American 

 forms as such, believing it to be introduced. After examining 



