454 Mr. T. D. A. Cockerell on Fossil Arthropods 
generic limits since Oligocene times. There are, of course, 
many extinct genera of Tertiary Diptera, but these have 
simply died out, and the fauna as a whole has not been 
transformed. 
In the Miocene of Florissant, Colorado, extinct genera of 
Diptera are rather numerous, and, in particular, there is a 
whole series of extinct types of Bombyliide. So far as the 
Gurnet Bay Diptera have been investigated, no trace of such 
a series of extinct genera has been found. The extinct 
Dipterous genera described (in former papers) from Gurnet 
Bay are Paltostomopsis (Blepharoceridee), bibiodites (Bibio- 
nidw), Protoberis (Stratiomyide), Stenomyites (Ortalidide), 
and Protoscinis (Chloropide). Another supposed extinct 
genus proved to be synonymous with the rare living genus 
Styringomyia. More than once, during Tertiary times, 
migrations have brought numerous elements of the Old 
World fauna into direct conflict with that of America. It 
seems probable that in the struggle fur existence whole 
groups of American genera, as in Bombyliidz and Aphidide, 
perished. Was there any corresponding phenomenon in 
Europe? The Gurnet Bay fossils do not suggest it, although 
some of the genera (of ants and termites) most abundantly 
represented in individuals have retreated to the Oriental and 
Australian regions. It must be said, however, that all the 
bees in Baltic Amber (Oligocene) belong to extinct genera. 
It remains uncertain whether they perished on account of 
the competition of other types migrating from elsewhere, or 
whether (as seems more likely) the whole bee-fauna has 
undergone evolutionary advance comparable with that of the 
mammals. In that case, the bees constitute an exception to 
the general statement made above. 
During October, my wife and I visited the Isle of Wight 
for the express purpose of examining the loéality of the 
insect beds. Following the directions kindly supplied by 
Mr. G. W. Colenutt of Ryde, we had no difficulty in finding 
the principal locality, which is at the junction of Gurnet (or 
Gurnard) and Thorness bays, in the Bembridge beds. The 
exposure of insect-bearing rock was on the shore, and was 
entirely worked out by Mr. A’Court Smith in the course of 
a uumber of years. So far as can be seen, it will never 
again be possible to make a large collection of Gurnet Bay 
fossil insects. All we could find consisted of stray pebbles 
on the shore, which on being broken showed the characteristic 
surfaces, with ants (principally G’cophylla) and in one case 
an undescribed Homopterous insect. There appears to be 
no douot whatever that the insect-bearing rock belongs to 
