174 BRITISH CICADiE. 



species discovered are, as yet, only represented by 

 single specimens ; and another is, that these species 

 can be recognized only as belonging to a single 

 locality. Insect areas in America, it is true, are 

 sometimes hundreds, if not thousands, of miles apart. 

 The circumstance that these insects do not simulta- 

 neously occur, leads Mr. Scudder to the supposition 

 that these deposits may not be altogether synchronous. 

 From the many thousand insects passed under ex- 

 amination, one might have expected the recurrence of 

 certain species ; but amongst the Hemiptera, at least, 

 such recurrent forms do not often appear, a circum- 

 stance which indicates the extreme richness of the 

 insect fauna of this period. 



An inconsiderable proportion of these fossil Hemip- 

 tera can be referred to genera now extant. " In many 

 cases, throughout whole groups, kindred differences 

 from modern types are found, which indicate con- 

 siderable changes of structure in the intervening 

 epochs along parallel lines." Special attention, inci- 

 dentally, may be called to the structural differences 

 between modern and fossil Aphides. 



The Tertiary basin of Florissant is situated in 

 Colorado. It is a small fresh- water lake, of about 2500 

 metres, equal to nearly 8200 feet above the sea-level, 

 surrounded by granitic, trachytic, and other volcanic 

 rocks ; or by grey or drab-coloured shales. These in- 

 sectiferous shales are composed of the finest sand or of 

 volcanic dust. Their total thickness may be 15 metres, 

 or say 50 feet. But the chief fossil riches have been 

 taken from the strata of one of the small islets, on the 

 shores of which originally grew gigantic trees, apparently 

 Sequoias, the trunks of which are still standing, and 

 show a diameter of 4 metres, or more than 13 feet. A 

 stratum of 46 centimetres in thickness has furnished 

 the largest number of insects ; but other grey or 

 " light-drab paper strata" are insectiferous, and they 

 have been successfully worked. Some of these strata 

 appear to have been cracked by the sun's heat, which 



