OF THE PAST. 



211 



About eighty palaeozoic species have been published up to the 

 present time, and have been grouped in two sub-families and 

 thirteen genera. Besides these, Brongniart has not yet given 

 any hint of how many have been found at Comrnentry, a 

 French locality which may be expected to increase the number 

 largely, and about twenty undescribed species are known to me 

 from the American Carboniferous rocks. 



The two tribes or sub-families differ in the structure of the 

 mediastinal vein ; in one type (Blattinarice) the branches part 

 from the main stem as in the other veins, at varying distances 



Fig. 120. Etoblattina mazona, Scudd. x 3. (The outline of natural size.) 



Carboniferous, Illinois. 



along its course (see the figure of Etoblattina) ; in the other 

 (Mylacridce) they spread like unequal rays of a fan from the 

 very base of the wing (see the figure of Mylacris). What is 



