134 Origin of the Araneidal Fauna of Yorkshire. 
widely distributed and abundant forms not only in all parts 
of Britain, but also over wide stretches of land both in the | 
Palearctic Regions of the Old World and very often of the 
Nearctic Regions of the New World as well. As examples of 
this group it will be sufficient to mention Tegenaria derhamit 
Scop., Phyllonethis lineata Clerck., Stemonyphantes lineata 
Linn., Linyphia clathrata Sund., Leptyphantes leprosus Ohl., 
Bathyphantes concolor Wid., Evrigone dentipalpis Wid., Xysticus 
cristatus Clerck., Philodromus aureolus Clerck., Tetragnatha 
extensa Linn., Pachygnatha degeert1 Sund., Meta segmentata 
Clerck., Zilla x-notata Clerck., Epeira diademata Clerck., Pirata 
piraticus Clerck., Lycosa amentata Clerck. 
Of one well known member of the group, Pisaura mirabilis 
Clerck., only two examples, both females, have so far been 
met with in the county. It has, however, a similar restricted 
distribution in some other localities. 
SOUTHERN GROUP.—tThe spiders comprised in this division 
are common across the centre and south of Europe and in the 
south of England. The comparatively few species which reach 
the county such as Prosthesima latreille: C.L. Koch., Amau- 
vobius ferox Walck., Episinus truncatus Walck., Theridion 
vittatum Koch., Erigone graminicola Sund., Enidia cornuta 
BI., Entelecara acuminata Wid., Xysticus Kochi Thor., and 
sabulosus Hahn., Oxyptila praticola C. L. Koch., Philodromus 
dispar Walck., Micrommata virescens Clerck., Pirata hygrophilus 
Thor., Heliophanus flavipes C. L. Koch appear in greatly 
diminished numbers, and do not penetrate much farther north. 
Their history may be said to date back at least to the 
Miocene Period, so that they are older geographically than the 
Northern species. The temperature of the N. Hemisphere was 
then much higher or more equable than at present and plants 
and animals belonging to warmer climates flourished within 
a short distance of the N. Pole. The gradually but surely 
increasing cold which succeeded this period, culminating in the 
Glacial Epoch, forced the various organisms southwards, the 
southern species now so called finally becoming located in regions 
beyond the regions of glaciation. The return of a more genial 
climate and the disappearance of the ice-covering would lead 
to a movement being inaugurated to reoccupy the newly 
exposed surface as soon as it became habitable, so that members 
of the group would be amongst the earliest to enter some parts 
of Britain; but in all probability not Yorkshire, as their 
northward advance would be greatly retarded by their incap- 
acity to withstand the decreasing temperature and the com- 
petition of others more fitted to endure the severer physical 
conditions of land just emerging from its ice-covering. 
SouTH WESTERN OR LUSITANIAN GROUP.—The fauna of 
the county naturally from its geographical position contains 
Naturalist. 
