NO. 1487. NORTH AMERICAN DIGGER WASPS—FERNALD. 803 



About halfway or a little less from the metacoxa to the stigma a 

 faint horizontal ridge or line may be seen, extending forward till it 

 joins the posterior metapleural suture or line, often at the bottom of 

 a small depression. In forms where the stigmatal line is absent this 

 line may sometimes be traced l)ackward to the petiole, its course being 

 a little above where the stigmatal groove would be in that region if it 

 were present. This line l)etween the stigmatal groove and the pos- 

 terior metapleural line may Ije regarded as marking the line of separa- 

 tion between the lower part of the metapleuron and the pleuron of the 

 median segment, which would lie dorsal to this line, anterior to the 

 stigmata] groove, posterior to the vertical part of the metapleuron, 

 and below the front part of the dorsum of the median segment. 



The petiole is cylindrical, ver}- slender, varying in length, and may 

 either be straight or curved, the arch of the curve when this occurs 

 being downward. At its ))ase above is a small levator muscle or funic- 

 ulus which is quite noticeable. Measurements of the length of the 

 petiole are often difficult to obtain, as the posterior end of the median 

 segment is frequently densel}^ covered with long hair. The measure- 

 ments of the petiole used in this paper are for this reason taken from 

 the posterior end of the levator muscle to the point on the dorsal sur- 

 face where the abdomen begins to enlarge and turn dorsally. 



The part of the abdomen behind the petiole is more or less ovate in 

 form, most pointed at the tip in the females, in which sex six segments 

 are perceptible. The dorsal plate of the tirst segment rises sharply 

 from the petiole, the angle var3'ing, the plate being nearly or quite per- 

 pendicular to the petiole in some cases. The stigmata of this plate may 

 lie in front, in the middle, or behind the middle of the plate, a char- 

 acter useful in subgeneric determinations. The other segments, except 

 the sixth (terminal) usually have no structural features of importance 

 in the female. The ventral plate of the terminal segment in this sex 

 is frequently longer than the dorsal one, and just above its tip the 

 sting ma}^ be protruded. In other cases the two plates extend an equal 

 distance. The outline of the posterior edge in these plates varies and 

 is a useful systematic character, as are also groups of hairs on the ven- 

 ti'al plates of these segments. The sixth ventral segment is frequentlv 

 quite strongly arched laterally, and in Palniodes it is even compressed, 

 so as to give a median longitudinal ridge which forms an edge between 

 the two sides of this plate. 



In the male the abdomen is less pointed behind than in the female 

 and is more or le.ss curled downward near its tip. Seven segments are 

 perceptil)le on its upper side, and eight beneath. The tirst four dorsal 

 plates are quite large and are wider from front to rear than the others. 

 The outline of the posterior edges of the hinder dorsal plates, particu- 

 larly of the last, is of importance. Beneath, the first four plates are 

 also larger than the others, the tifth, sixth, and seventh being much 



