FOSSIL HEMIPTERA OF THE LIAS. 149 



Professor J. W. Westwood believed that most of 

 these insects were aquatic in habit, and that they 

 affected the neighbourhood of fresh- water streams, 

 over which they hovered during life and became sub- 

 merged after death. 



The last author remarks : — " It is scarcely to be 

 supposed that a state of things could have existed in 

 which we should find such a collection of insects as the 

 Wealden [Purbeck] series exhibits, without there being 

 parts of the world inhabited by giant Cicada?, immense 

 beetles, locusts, and grasshoppers, with wings expand- 

 ing little less than a foot, and other insects of the 

 size at least of those of the present creation."* 



Elsewhere he says : — >" It is not an invariable rule ; 

 but climates of low temperature produce insect forms 

 of small dimensions. The presence of Aphides in the 

 Wealden beds leads to the supposition that the exist- 

 ing climate was that of a warm temperature rather 

 than that of a subtropical character." 



Discoveries of fossil Aphides have hitherto been 

 comparatively rare, and perhaps the reasons are not 

 difficult to find. Independently of the delicacy of 

 their structure and their minuteness, the circumstance 

 that a mild and temperate climate seems necessary to 

 their existence must limit their horizon, and also the 

 area possible for their preservation. 



In present times, as a rule, under tropical heats 

 Cicadidee and Fulgoridse take the places of Aphididse. 

 Again, it is pretty obvious that those Aphides inhabit- 

 ing swamps and the banks surrounding still waters 

 were the most suited for preservation. The finest muds 

 and sediments are requisite to yield obvious impres- 

 sions, and moreover sucli sediments must be very 

 rapidly deposited to prevent the disintegration of frail 

 insects. Accordingly we find that the fresh-water 

 beds of (Eningen, within the valley of the Rhine, and the 

 basins of the ancient lakes of Florissant in America, 

 are the localities which up to the present time have 



* ' Quart. Journ. Geol. Soc. Lond.,' vol. i, p. 400, 1845. 



