OF THE PAST. 



217 



genera of the Trias are peculiar to it. So, too, are some of the 

 genera of the Oolite, but all of the Liassic genera occur also in 

 the Oolite. 



Among these mesozoic Cockroaches are some of very peculiar 

 aspect; one, Blattidium (see figure of B. Simyrus), found only 

 in the lower Purbecks, has ribbon-shaped wings with parallel 



Fig. 124. Blattidium Ximyrus Westw. X 3. Lower Purbecks, England. 



sides, longitudinal neuration, and anal nervures with a course 

 at right angles to their usual direction ; another, Pterinoblattina 

 (see figure of P. intennixta), geologically widespread, is very 

 broad, more or less triangular, and has an exceedingly fine and 

 delicate neuration, so arranged as to resemble the barbs of a 

 feather. 



A comparison of the neuration of the tegmina of mesozoic 

 and recent Cockroaches, to determine as far as possible the 

 immediate relations . of the former to existing types, gives 

 as yet little satisfaction. The prolific genera, Mesoblattina and 

 Rithma, may be said to bear considerable resemblance to the 

 PhyttodromidcBj and the peculiar neuration of Elisama is in part 

 repeated in the Panchloridce, as well as in some PhyUodromidce 



