AND OTHER INJURIOUS INSECTS OF I907 AND I908. 183 



mandibular lamina, about five hairs on the labrum, and none on the 

 first maxillary laminae. 



The Prothorax: The prothorax is usually short and of small 

 size, sometimes bent under the mesothorax so that it cannot be seen 

 from the dorsal side. But in other genera it is as long as it is broad 

 and nearly as large as the mesothorax. The undivided pronotum 

 usually bears a lateral tubercle on each lateral edge. Sometimes 

 there is only a single short spine-like tubercle, in other genera there 

 are several of these tubercles in a group. The episterum is a small 

 anterior rectangular thickened piece. The area of the epimerum is 

 not thickened ; it bears a spiracle and sometimes a tubercle. The legs 

 articulate with these two pieces and with the sternum which is small. 



The Mesothorax: The mesothorax is a large segment in all 

 plant lice. The tergum is plainly divided into praescutum, scutum, 

 scutellum, and post-scutellum. The praescutum is usually an equi- 

 lateral triangular piece with its base pointed forward. But in some 

 forms (Phyllo.vcra) it is rectangular and broader than it is long. The 

 large scutum is divided into two semi-circular halves by the apex 

 of the prsescutum and a mid-dorsal suture. The prominent scutel- 

 lum is about half as wide as the thorax and is sometimes divided 

 along the mid-dorsal line by a suture. The post-scutellum slants 

 backward and downward under the metatergum, so that very little 

 of it is exposed. It is broadly triangular with an obtuse apex point- 

 ing posteriorly. The sternum called thoracic plate is divided by longi- 

 tudinal and transverse sutures into four parts. The anterior parts 

 articulate with the episternum. In CalUptcrns the posterior prices 

 are much smaller than the anterior pieces. In Tctraneura the pos- 

 terior pieces are almost square. It is difficult to make out the epi- 

 sternum and epimerum of the mesothorax, but there is a T-shaped 

 suture on the side of the mesothorax which probably separates these 

 two regions. The anterior one is the region of the episternum, the 

 posterior one, the region of the epnnerum. 



The Metathorax: The metathorax is reduced and closely 

 fused with the mesothorax. The tergum is usually divided by a trans- 

 verse suture into an anterior and posterior parts. The region of the 

 episternum and epimerum cannot be made out distinctly. The sternum 

 is not thickened, except in some cases on its anterior border. 



The Wings: There is need of homologizing the wing \eins ot 

 Aphids with the wing veins of other insects. The names given here, 

 based on Comstock's system, were decided upon from a study of other 

 reduced wings, such as those of Psocus, and from a study of the ab- 

 normal venations found so frequently in plant lice. 



