35 
By systematic palaeontological investigations like those of this 
paper two questions naturally arise, viz. how was the nature in 
which these forms lived? and what do they tell us about the climate 
of the period in which they lived? 
As to the first question, we must begin by stating that both 
terreslric and aquatic forms are represented in the 2 faunæ compared, 
(Rocky Mountains: Trichoptera, Odonata, several Nematocera; Diatom- 
earth: the Odonat and perhaps the craneflies). Whether the Danish 
aquatic forms have completed their development in the very lagoon 
in which the Diatom-earth was deposited or in pools on the firm 
land behind it, we cannot determine, and it, therefore, is of rather 
small interest to us. A comparison between the terrestric forms 
of the two faunæ is, on the other hand, most interesting. It namely 
distinctly displays a characteristic difference which may very well be 
designated by difference of facies, a word otherwise only applied 
to marine deposits. As far as America is concerned, we must 
especially call the attention to the many weevils and other beetles 
developing in wood which indicates that the surroundings of the 
American localities then were close to rich forests. The Diatom-earth 
insects, on the other hand, the Planipennids, Fulgorids, Moths etc. 
and above all the very great contribution of bugs, in a much higher 
degree belong to the open country than to forests; the range of the 
Diatom-earth insects thus obviously must be characterized as meadow 
near water. 
As regards the climate of the Eocene period several forms 
are suggestive of a tropical one. The Phenacolestes genus belongs to 
the Podagrion-gvoup, the living representatives of which all are 
tropical forms (tropical America, tropical Africa, the East Indies, Au¬ 
stralia). The cranefly genus Eriocera likewise belongs to the Tropics 
(South Amerika, Sumatra, Formosa) and the species group to which 
the Diatom-earth species belongs is specifically east Asiatic. All the 
Homoptera belong to the Fulgorids of which the main part, especially 
the large lepidopterous forms, belong to the Tropics; the family 
Ricaniidce to which two of the Diatom-earth forms have been refer¬ 
red consists of nothing but tropical insects (the Brasils, the Guinea 
coast, India, the East Indies, Japan, Australia etc.). This also applies 
to almost all the Flatids, the two Diatom-earth representatives of 
which must be referred respectively to the genera Lechœa , the two 
species of which occur in Borneo, Celebes a. s. f. and to Or men is 
the many species of which belong partly to tropical America, partly 
to the islands of South Asia (Ceylon, Sumatra, Java etc.). Finally 
the obviously common bug (3 finds of this species existing) Tectoc- 
oris angustilobatus must be named which appears to be tropical 
