US 



Sellartfs — Structure of Paleozoic Cockroaches, 



areas used in this paper is different from 

 that proposed by Pleer and employed 

 heretofore in the literature of American 

 paleozoic insects, it has been thought ad- 

 visable to introduce a sketch of the wing 

 of a typical member of the Paleoblat- 

 tidse, giving Redtenbacher's and Heer's 

 names in parallel columns. 



Terminology of the wing Terminology of the wing 

 veins as developed by veins applied by Heer 



Eedtenbacher. 



to cockroaches. 



1. Costa. 



Marginal. 



2. Subcosta. 



Mediastinal. 



3. Radius. 



Scapular. 



4. Media. 



Externomedian 



5. Cubitus. 



Internomedian. 



6. Anal veins. 



Anal veins. 



Figure 1. — Gerablal- 

 tina arcuata Sellards. 



Structure of Paleozoic Cockroaches. 



Head. — The head is small, flattened, and capable of being 

 withdrawn partly or entirely beneath the pronotum. The part 

 most commonly seen is the top, or top and front. The sutures 

 dividing the parts of the head are often discernible. The eyes 

 are placed well up toward the top. Their shape is obscured 

 by crushing, but they were large and apparently elongate or 

 reniform. The frons or clypeus posterior is occasionally 

 recognizable (Text-figure 9). The mandibles have not been 

 observed. Supposing them to have been as firmly chitinized 

 as at present, their absence where more delicate structures are 

 preserved is unexpected, and suggests the possibility that the 

 early cockroaches may have fed on soft vegetation, and have 

 had less strongly chitinized mandibles than their omnivorous 

 descendants. The antennas are long, slender, and many jointed. 

 They are enlarged at the base and united to the head by a cir- 

 cular socket-like attachment (Text-figures 4: and 19). 



Thorax. — The segments of the thorax, as in living generalized 

 insects, are not fused or closely united. The pronotum presents 

 considerable variation in shape in the different genera and 

 species, and goes through a regular series of changes during the 

 growth of the individual. At first the posterior border is 

 straight, the lateral angles pointed, and in the Mylacridse 

 directed backward. As growth progresses the corners become 

 less acutely pointed, then rounded, and the posterior border 

 fuller. The pronotum of the adults of the tribe Mylacridse is 

 always proportionately broad, but with a rounded posterior 

 border. Among the Blattinarise the modification progresses 



