1918] Thoracic Sclerites of Hemiptera 243 



(es) projects backward over it for some distance. With few 

 exceptions, notably in the Nabidse (Figure 24) and Cimicidse, 

 and possibly in some others, the coxae (ex) of all Heteroptera 

 are partially overlapped by the metapleural plates, the coxal 

 attachment (x) being concealed and its position not usually 

 recognizable externally. In Gerris (Figure 21), an elongate, 

 cylindrical form, the base of the coxa is set in a bulging socket, 

 as in the mesothorax, except that there is no cleft in this socket. 

 In Emesa (Figure 14), another elongate form, the base of the 

 hind coxa (cxs) is partly covered by a pointed flap, while 

 another pointed flap lies behind it. 



The pleural suture (ps), except in Corixa (Figure 19), Noto- 

 necta (Figure 16) and Belostoma (Figure 20) is absent in the 

 metathorax of all forms studied. A coxal cleft (cs) is often 

 present, as in the Nepidce, Berytidae (Figure 22), Coreidse 

 (Figure 23) and many other forms, but it is not to be homol- 

 ogized with the coxal cleft (C2) of the mesothorax, since it does 

 not terminate at the coxal process (x), but is usually located in 

 front of and below the coxa. Hence it is incorrect to use the 

 metathoracic coxal cleft (cs), as some writers, (Tower, 1914, for 

 example) have done, as a ''landmark" for separating epister- 

 num (esg) and epimeron (ems). The episternum (esa) and 

 epimeron (ems) are always to be separated by the pleural 

 suture (ps), and when this is absent, as it is in these forms, we 

 must take as a basis for the division of the pleuron, the two 

 points which are the constant limits of this suture when it is 

 present. Thus the episternum and epimeron can be exteriorly 

 separated only by an imaginary line, representing the pleural 

 suture, extending from the wing fulcrum to the articulation of 

 the coxa (x). This conclusion is strengthened by the fact that 

 on examination of the interior surface of the pleuron in certain 

 forms where no pleural suture exists, one will find a more or less 

 distinct ridge, extending in an irregular, but fairly definite line 

 between the wing fulcrum and the coxal process. Now in all 

 forms possessing a pleural suture there is to be found on the 

 inner surface of the pleuron a corresponding pleural ridge, this 

 ridge being the internal manifestation of the external pleural 

 suture. Hence it is not incorrect to use this ridge, which is as 

 constant as the suture, as a "landmark" in naming the pleural 

 plates. The ridge has been represented by a dotted line in the 

 figure of the squash bug (Figure 23). It would probably be 



