‘On the Diptera of the Amber-fauna. 309 
ground for their unfrequent occurrence in amber, if we assume 
that the species of these families were already abundant in the 
Amber epoch, while under the same supposition we could ex- 
Plain it by the controlling influence of special local conditions. 
he numerous and very varied forms of the Cecidomyda, whose 
species are strictly confined each to its peculiar plant, teach us 
that the flora was one rich in species; this decidedly removes 
the supposition of the exclusive presence of extensive conifer- 
lants, if not abundant in numbers, were at least rich in species, 
while it is by no means app 
cent form. Next to the Cecidomyide, the species of no other 
aes the rarity, of Synanthere in the Amber period, would 
these insects, who seek the plants, which are to be the r 
