i 



408 ENTOMOLOGICAL NEWS. [Nov.,'17 



and Apodidae, and at the bottom of this stem, the Trilobites 

 unite with the Crustacea, so that it is not surprising that 

 certain Trilobite features might have been retained in some 

 of the groups derived from their common ancestral forms. 

 My own observations would lead me to consider the closely 

 related Insects, Isopods, and "Myriopods" as derived from 

 Arthrostraca-like ancestors, which in turn were derived from 

 lower Crustacean forms ultimately related to the Trilobites, 

 rather than to regard insects, etc., as descended more directly 

 from Trilobite forebears, as certain recent investigators would 

 maintain is the case. These points, however, can be more 

 profitably discussed elsewhere. 



The more intimate relationships of the insects considered in 

 the foregoing discussion may be expressed by grouping them 

 into three superorders as follows : The Blattoid, Mantoid. and 

 Isopterous insects form one superorder (the Pandictyoptera), 

 in which the head is typically (though not always) hypogna- 

 thous, the lateral cervicals touch in the median ventral line, and 

 the ventral cervicals, when present, are situated far forward, 

 and occur as two narrow transverse bands somewhat crescent- 

 shaped in outline. A fold of the posterior margin of the tergum 

 projecting backward in two more or less pointed projections 

 (the postplica) usually occurs in both meso- and metathoracic 

 terga, and when the scutellum is demarked, it is usually nar- 

 row and extends far forward into the scutal region. The meso- 

 thoracic coxae are usually much longer than broad, and the 

 tarsi are typically pentamerous. Ovipositor present in some, 

 absent in others. Styli present in some males. 



The Embioid, Forficuloid and Plecopterous insects form the 

 second superorder, the Panplecoptera, in which the head is 

 typically prognathous, the lateral cervicals do not touch in the 

 median ventral line, and the ventral cervicals instead of occur- 

 ring as narrow transverse bands situated far forward in the 

 neck region, are much broader and the posterior one occurs 

 just in front of the prosternum. The mesothoracic coxae are 

 usually as broad as long, tending to have a ring-like outline 

 \vhen viewed from the mesal surface, and the tarsi are typically 

 trimerous. Ovipositor and styli usually absent. 



