10 
Cockerell: Eocene Fossils from Green River, Wyoming. Amer. 
Journ. of Sei. (4) XXVIII. 1909 p. 447. 
Cockerell: Some American fossil Insects. Proc. U. S. Nat. Mus. 
LI. 1917 p. 89—106. 
Cockerell: New Tertiary Insects. Proc. U. S. Nat. Mus. LII. 
1917 p. 373—84. 
Cockerell: New Species of North American fossil beetles, coch- 
roaches and Tsetsetlies. Ibid. LIV. 1919. 
Cockerell in Nature 20 March 1919 p. 44. 
Cockerell in The Entomologist 1919 LII p. 122 l ). 
Cockerell: Eocene Insects from the Rocky Mountains. Proc. U. 
S. Nat. Mus. LVII. 1920 p. 233—60. 
Cockerell: Some Eocene Insects from Colorado and Wyoming. 
Proc. U. S. Nat. Mus. LIX 1921 p. 29—39. 
Cockerell and Grace Sandhouse: Some eocene Insects of the 
family Fulgoridae. Ibid. LIX. 1921 p. 455—57. 
As will be seen from my determinations in the following, a 
comparison between my material and the Eocene insect forms previ¬ 
ously known has not been of much importance. The determination 
of European finds is for the greater part insufficient, and the species 
described are so few that it is not likely that new finds belonging 
to a group so rich in species as that of the insects might be referred 
to the few European ones described, and the Rocky Mountain fauna 
of which a considerable number of species has been described is 
— as above mentioned — geographically too distant from us to be 
of any special use. 
It has turned out that a critical use of the much more thoroughly 
based systematics of the recent insects yielded good hints as to the 
systematic reference of examined forms, and for this purpose I, 
therefore, have made use of the literature dealing with these recent 
systematics, as well as of the recent forms proper, in so far as they were 
represented in the collections of the Copenhagen Zoological Museum. 
As species of hitherto known Eocene insects are so few, as said 
above, it is no wonder that all the forms, referred to species by me, 
have turned out to be novæ species to science. Some specimens, 
especially a number of Hemiptera I have only referred to families. 
Though I was well aware that at any rate the greater part of these 
Hemiptera cannot be referred to previously described fossil forms, I 
have not been able to find any “characteres essentiales” (to use a 
Fabrician term) by which with certainty to refer eventual further finds 
9 I have not seen this paper. 
