Origin of the Araneidal Fauna of Yorkshire. 133 
fauna of the county, for besides being constitutionally the best 
fitted to endure more rigorous climatic conditions, the arrange- 
ment and continuity of the mountain ranges in Scotland and 
the North of England would be favourable to their rapid 
extension, even at a time when the lower lying land would be 
impassable to species advancing from other directions. 
WESTERN GRoOuP.—The next group to enter Yorkshire 
embraced those species which spread into it from a westerly 
point of the compass, for if the land connection between 
Ireland and Gt. Britain, while co-existent for a time with, was, 
as some geologists suppose, anterior both in point of elevation 
and submergence to that between S. E. England and the 
Continent, thus affording earlier access from the west, and if, 
as paleontology indicates, a warmer climate prevailed then as 
now in the western portions of Britain than in the eastern, then 
the former would most likely be sooner in a condition to support 
an araneidal population than the latter. The western species 
would slowly diffuse as the physical conditions improved suffici- 
ently to permit it, but their progress would no doubt be ham- 
pered not only by the change of temperature incidental to 
passing from a more insular to a more continental climate but 
also by less tangible but not the less effective obstacles, for at 
a later period they would find themselves in contact with other 
species, much more vigorous, much more tolerant of crowding 
and competition, not exactly cold fearers or particular as to 
habitat and moreover favoured by improving climatical 
conditions as they spread towards the more insular areas. As 
a result of the ensuing competition, either all the Western 
species did not reach the Continent, or the severance of the land 
connection left their advance guard in such disadvantageous 
circumstances that they have either been wholly or partially 
displaced there, only now occurring in some of its western 
countries and very rarely indeed extending farther east. They 
have however maintained their ground in the British Isles and 
in some parts of them are common. The following rarer mem 
bers of our fauna are probably referable to this group ; Onesinda 
minutissima Camb., Halorates reprobus Camb., Bathyphantes 
setiger F.O.P. Cb., Syedra innotabilis Camb., Gongylidiellum 
paganum Sim., Lophocarenum mengit Sim., Diplocephalus 
protuberans Camb., Entelecara thorellii Westr., Baryphyma 
pratensis Bl., Oxyptila flexa Camb. More unmistakable and 
commoner members are Oonops pulcher Templ., Amaurobius 
similis Bl., Hahnia montana Bl., Leptyphantes blackwallit 
Kulcz, Erigone promiscua Camb., etc. 
EASTERN OR CONTINENTAL GROUP.—The spiders belonging 
to this section entered our area from the south-east and they 
are those dominant and vigorous species which were referred 
to when dealing with the western section. They are the most 
1g13 Mar. E 
