PROC. ENT. SOC. WASH., VOL. 22, NO. 5, MAY, 1920 99 



the relative sizes of the basal segments of the antennae, the Zor- 

 aptera exhibit certain features peculiar to themselves. 



The neck plates and prothoracic sclerites "dc," "Ic," etc. (Fig. 

 1) of a winged '/.orotypus, are extremely like those of Capnia, and 

 other primitive Plecoptera, especially in the occurrence of the 

 peculiar dorsal cervical sclerite "dc;" and since the neck and pro- 

 thoracic regions are among the least modified structures of an 

 insect's body, they furnish some of the most valuable evidence 

 available for determining the interrelationships of the orders of 

 insects. In order to show the outlines of the sclerites as well as 

 possible, an abnormally distended specimen was chosen for mak- 

 ing the drawing shown in Fig. 1 , so that the parts are considerably 

 more separated from one another than would be the case in a 

 normal specimen; but a glance at Fig. 1, after studying a primitive 

 Plecopteron such as Litctra or Capnia, would serve to convince 

 one that the neck and prothoracic regions of a winged Zorapteron 

 are strikingly like those of the primitive Plecoptera in question; 

 so that the evidence of the head, neck and prothoracic regions 

 alone, would point to a very close relationship between the Zor- 

 aptera and the Plecoptera. On the other hand, the mesothoracic 

 and metathoracic structures present a curious combination of 

 features occurring in the Psocidae, Isoptera, Grylloblattidae, and 

 certain insects related to the Plecoptera. 



The mesonotum and metanotum of Zorotypus (Fig. (5) are very 

 like those of the Psocidae in some respects, such as the outline 

 of the prescutum "ps 2 ," scutellum, "sc! 2 ," etc.; and the presence 

 of a prealar bridge "pa" extending from the notum to the pleural 

 region (see also "pa 2 ," Fig. 1) is a feature which occurs in the 

 Plecoptera and their relatives, as well as in the higher insects, 

 but is not found in any of the group to which the Isoptera belong 

 (i. e., the Mantidae, Blattidae, etc.), as is also true of the pres- 

 ence of a postscutellum, "p 2 " (Fig. 1) in the mesothoracic region. 

 A mesothoracic postscutellum, however, occurs in the Plecoptera 

 and their relatives, as well as in the Psocidae and higher insects. 

 In the Blattidae, Alantidae, Isoptera and many other lower in- 

 sects, there is a marked tendency for the metanotum to surpass 

 (or at least to equal) the mesonotum in size; but in the winged 

 Zoraptera (Fig. 6), the mesonotum is markedly larger than the 

 metanotum, as is also the case in the Psocidae and higher forniN. 

 In general, the mesonotum and metanotum of the winged Zor- 

 aptera are very suggestive of those of the Psocidae and higher 

 insects; but the outlines of the nota of the wingless Zoraptera un- 

 surprisingly similar to those of the wingless Grylloblattidae. 



The sternal regions of the thorax of the Zoraptera are quite 

 like those of the Isoptera, and similar lateral plates, or latero- 



