The Distribution of Spiders in the East Riding. 283: 
uno disce omnis,’ we may cover over some of the unworked 
gaps in the map. 
Changes in the distribution of animal and plant life are 
necessarily always taking place, even in the natural course: 
of events, but these changes are intensified (too often on the 
side of extermination), by drainage, deforestation, military 
works, building and other manifestations of the activities of 
civilised communities. Moreover, long established species may 
be overlooked for many years and the occurrence of some 
form discovered by mere Juck—usually by an outsider—is 
liable to upset one’s pet theories. Further, additions are: 
constantly being made through natural or accidental means 
of dispersal. Thus in matters of distribution there is no 
finality owing to changes on both the plus and minus sides. 
Quite large numbers of spiders are of common occurrence: 
over the whole area, provided they are searched for in their re- 
spective habitats, and this number will probably be still further 
increased as more attention is devoted to collecting. For 
example, under the bark of trees or in crevices of fences can 
always be found Segestria senoculata, Amaurobtus fenestralis, 
Epeira umbratica and Salticus cingulatus ; while every field 
and open space is coursed over by myriads of the Wolf Spiders, 
Lycosa amentata and L. pullata. Atiecting human habitations. 
and outhouses are such forms as Amaurobius similis, Tegenaria 
derhamiit (par excellence our domestic species), and Zilla 
x-notata ; while every ditch, drain and pond side is frequented by 
Pirata pirvaticus, Clubiona holosericea and Emidia bituberculata. 
On the other hand are species which occur only in a limited 
area, and there perhaps commonly. These are forms specialised 
for life under particular conditions related to either the native 
food supply or soil, relative salinity, or to some indefinable 
cause, and unable in some cases to adapt themselves to even 
slight changes of habitat. 
In investigating the subject of localness of species, puzzling 
facts come to light. How is it, for instance, that Hyctia 
nivoyi and Clubiona subtilis, both abundant species on the 
sandhills at Spurn and the Humber shore at Easington, are 
not found elsewhere in the vicinity of the dunes, nor indeed 
in any other Yorkshire locality, although in other parts of the 
country, as at Wicken Fen, they inhabit a totally different 
habitat ? 
For our present purpose the East Riding may be conveni- 
ently divided into the following eight areas :— 
(1) Hurt.—It is of interest to know the spiders to be 
found in a large city. In addition to those characteristic of 
‘human habitations, cellars, warehouses, etc., are species which 
may be introduced by the agency of trade and commerce ; 
1916 Sept. 1. 
