Scudder.] 
568 
[ April 2, 
genera, Palecphora, Lithecphora and Palaphrodes, with their fif- 
teen species, not only outnumber in specific types the other seven 
genera of Cercopidae (twelve species), but they contain more than 
nine-tenths of the individuals of this family which have passed un- 
der my eyes. 
A few points of special interest may be found on examining some 
of the separate families. Thus one would hardly suppose that ob- 
jects of such extreme delicacy and minute size as plant lice would 
be found in a fossil state. Yet they are by no means infrequent, 
and have even been found in the secondary deposits of England ; for 
in Brodie’s work two objects which appear to be wingless forms are 
figured, and besides these another winged plant louse of a diminutive 
size, showing the characteristic venation of the group ; while in the 
tertiary rocks a considerable number of species have been found ; 
most of these have been referred to Aphis (twelve species) and 
Lachnus (eight), and so belong, like the bulk of living species, to 
the subfamily Aphidinse. But the Pemphiginge are represented by 
a Pemphigus from Oeningen, and the Schizoneuringe by a Schizo- 
neura from amber. Besides occurring in these localities, they have 
also been found at Radoboj, Aix, and Ain in Europe, and we can 
now a,dd several localities in our own country. 
That they are not scarce in amber is shown by Menge’s collec- 
tion which in 1856 included fifty-six specimens. But these are 
few compared with the number from Florissant where more than 
one hundred specimens have been found, about seventy of them de- 
terminable, though in the other American localities, Green River, 
in Wyoming, and Quesnel, in British Columbia, only two or three 
specimens have occurred. Indeed, by the publication of the Ameri- 
can forms the number of known fossil species is doubled. 
There are some remarkable features about the Florissant forms. 
The mass of them belong, as is the case with those from the Euro- 
pean tertiary rocks, to the Aphidinse proper. But both here and 
in the Schizoneuringe to which the remainder appertain, we are met 
by two remarkable facts : one that the variation in the neuration of 
the wings is very much greater than occurs among the genera of 
living Aphidinge and Schizoneuringe, and greater also than occurs 
in the known tertiary forms of Europe, requiring the establishment 
of a large number of genera to represent this variation ; and, sec- 
ond, that at the same time there is one feature of their neuration 
in which, without an exception, they uniformly agree, and differ, 
