HEMIPTERA— HOafOPTERA— COCCID^. 241 



This table shows clearly how poorly the Aphides and Fulgorina are 

 preserved in the European as compared with the American rocks. 



It has been necessary to establish a large number of new generic groups 

 to contain the American forms, which perhaps would not have been the case 

 to the same extent had a really good selection of existing tropical American 

 types been accessible ; for the affinities of nearly the whole homopterous 

 fauna of our Tertiaries are plainly subtropical. It is curious to see how 

 highl}- developed some apparently extinct types were in that day ; the family 

 groups were quite as trenchant as now, and while we find in some, as in 

 Aphides, marked departures from modern structure, it in no way appears to 

 affect the family characters or to mark any approach toward the neighboring 

 groups. Some genera now apparently extinct seem to have attained a high 

 degree of differentiation, as witness Aphidopsis among the Aphides, Dia- 

 plegma among the Fulgorina, Palecphora, Lithecphora, and Palaphrodes 

 among the Cercopidse ; of all of these there were several species, and more 

 than occur in any other generic group excepting Agallia among the Jassides, 

 which is equal to the least prolific of them. As a general rule it is also in 

 just these genera that the individuals are the most abundant, notably among 

 the Cercopidse, which as a family is almost twice as numerous as all the 

 others together, though the least among these larger families well provided 

 with generic distinctions ; for the three genera, Palecphora, Lithecphora, and 

 Palaphrodes, with their fifteen species, not only outnumber in specific types 

 the other seven genera of Cercopidse (twelve species), but they contain more 

 than nine-tenths of the individuals of this family which have passed under 

 my eyes. 



Family COCCI D^E. 



The only fossils of this group hitherto known are some that occur in 

 amber. Three species referred to Monophlebus were described and figured 

 by Grermar, and Menge has since added short descriptions of half a dozen 

 species referred to Aleurodes, Coccus (2), Dorthesia, and the extinct genera 

 Ochyrocoris and Polyclona. To these we are able to add a single species 

 from Florissant. 



MONOPHLEBUS Leach. 



This is an Old World genus which has never been detected living in 

 America. The species are largely from tropical regions, but a single one 

 is recognized from Europe. On this account there is special interest in the 



VOL. XIII 16 



