110 HYMENOPTERA. 



no doubt about its being a mere form of P. cressoni which is 

 poorly pigmented. In genital, and sculptural characters, as 

 well as size and form, it agrees perfectly with P. cressoni, 

 unless a slight modification of the eighth ventral plate is 

 characteristic. In the only specimen at hand this plate has 

 apical lobes that lack the granular appearance of the typical 

 specimens, and are somewhat flattened, (fig. 51), but I think 

 this is very likely due to the individual mount. The face 

 marks of this form are obviously of the same type of those 

 of the typical form, the only diflference being that they are 

 incomplete, so in such a variable group as this it would be 

 folly to give it specific rank. This conclusion is made even 

 more certain by the fact that the females are indistinguish- 

 able from those of the typical form. I have a complete 

 series of these showing a perfect gradation, or rather show- 

 ing all the intermediate variations, from this to the more 

 strongly marked forms, and even some in which there is 

 practically no yellow pigmentation whatever. With such 

 series as these to examine there can be no doubt about the 

 specific identity of the various specimens which have been 

 considered distinct. 



Aside from the forms given above which can be in some 

 cases distinguished from the typical specimens, are two 

 " species " which can not even be separated as forms. 

 These were described as P. pasadetKZ Ckll. and P. labiati- 

 h'ons Ckll. Of the former I have specimens determined by 

 Professor Cockerell and a large series from around Pasadena, 

 the type locality, all of which are indistinguishable from the 

 series of typical specimens. As to the identity of the latter 

 I am not so sure, as I have no specimens, but it is indistin- 

 guishable by the description, at least. It is described as dif- 

 fering from P. cressoni by its larger size, which might indi- 

 cate P. rudbeckicz, but as Professor Cockerell described this 

 also, I infer not. P. cressoni varies so markedly in size that 

 no distinction can be made on this alone, and unless new 

 characters are obtained from the type it will certainly have 

 to remain under P. cressoni. 



Among the various series of P. cresso?ii I have come upon 



