1918] Thoracic Sclerites of Hemiptera 237 



DESCRIPTION OF A GENERALIZED HETEROPTEROUS THORAX. 



Suborder Heteroptera, Family Belostomatidas; Belostoma americana, 

 Zaiiha sp. Figures IS and 20. 



The giant water bug {Belostoma americana) is described 

 rather fully here, since it is a somewhat generalized Heterop- 

 teron. It is also of a convenient size to study and it is widely 

 distributed. 



Prothorax. 



This segment, as in most Heteroptera, is somewhat collar 

 like, fitting tightly to the head and closely overlapping the 

 anterior part of the mesothorax. The notum is trapezoidal in 

 outline and is rather large. The pleural region is somewhat 

 broad above, narrowing to meet the narrow sternum. Rarely 

 is the prothorax distinctly marked off into sclerites, and it is 

 fundamentally so similar in all Heteroptera, that it will require 

 but little mention. 



Mesothorax. Figure 18. 



Notum. The notum of the mesothorax does not show a dis- 

 tinct pretergite, this sclerite being probably represented by part 

 of the anterior phragma (aph). The prescutum (psc), a semi- 

 circular piece, is marked off clearly. Extending in front of the 

 wing from the lateral margin of the prescutum is a bilobed 

 prealare (pra), the anterior lobe of which joins an upward pro- 

 jection of the sternal region. No separating suture occurs 

 between scutum (sc) and scutellum (si). The latter is produced 

 backward to a point over the metanotum. A postscutellum 

 (psl) is concealed under the scutellum and is connected by the 

 postalare (poa) with the epimeron. Snodgrass, 1909, at first 

 stated that no postscutellum was present in the mesothorax of 

 of Belostoma. Later (Snodgrass, 1910), however, he noted the 

 presence of this sclerite. 



Pleuron. The mesopleuron in this and in other Heteroptera 

 has the appearance of having been distorted from its normal 

 form, i. e., the upper part seems to have been pushed forward, 

 or the lower part backward. This brings about two remarkable 

 conditions: first, the pleural suture (p) becomes almost hori- 

 zontal, and second, the coxa (ex) extends outward from the 

 rear of the segment instead of from beneath. Another peculiar- 

 ity of this and other members of the suborder is the overlapping 

 of the base of the coxa by the lower parts of the two pleural 



