J. C. HUTSON 213 



the petiole proper the appearance of being cut off obhqiiely, and 

 the intervening space between its posterior edge and the anterior 

 dorsal edge of the second abdominal segment is covered over by a 

 roundly convex plate. This plate may be regarded as the true 

 notum and is hinged to the petiole proper along its anterior 

 dorsal edge by a thinly chitinized strip, thus allowing consider- 

 able flexion along that region. The notum sends down a flap on 

 each side, which extends below the edge of the sternum but is 

 connected with it on the inner side by a membrane, so that the 

 lower portion of the flap is free on each side. The posterior 

 margin of the notum widens out to fit over the anterior margin 

 of the second abdominal segment, and between the two plates is 

 a thinly chitinized strip similar to those found between any two 

 other abdominal segments. 



The modification of the petiole may be interpreted as follows. 

 The cj'lindrical portion is possibh' the result of the gradual curling 

 up of the sternum and pleuron on each side and the ultimate 

 dorsal fusion of the pleura to form a solid tube. During this 

 process the notum appears to have been gradually pushed back- 

 wards, until it finally came to occupy its present position as a 

 convex plate fitting over the distal end of the cylinder. The 

 above is only a brief suggestion as to the process through which 

 the petiole may have passed in order to reach its present highly 

 specialized condition, but this subject is of sufficient interest to 

 be worked up from a morphological standpoint. 



The portion of the abdomen behind the petiole is of normal 

 size, widening suddenly to a somewhat ovate form. In females 

 the tip of the abdomen is dorso-ventrally flattened to a blunt 

 point, while in males the tip is more or less truncate and curved 

 under. In females six segments are visible dorsallyand ventrally, 

 while males show seven on top and eight below. The spiracles 

 are on the anterior dorso-lateral portion of the segments and occvu' 

 on all the segments in females and males, but usually only those 

 on the first two segments are visible in pinned specimens. The 

 third and fourth ventral segments of the female may or may not 

 have pubescent spots on their ventral surfaces, and the posterior 

 margin of the third ventral segment may be sinuous or almost 

 straight, according to the species. In males the fourth and fifth 



TRANS. AM. ENT. SOC, XLV. 



