KKNDAl.I. : THE MOLLUSCA OF OUNDI.E. 249 



§ I. a. Osier Beds. 



This type of woodland, a very noticeable feature of the landscape, 

 is included in the Alder-Willow Series. Examples are found frequently 

 along the course of the river, some in use and regularly cleaned and 

 harvested, while others consist of ragged clumps of trees which have 

 sprung from the old stools. Being practically at river-level, they are 

 all liable to flooding and permanently moist. Very rich in molluscan 

 life, they have their own peculiar association. 



Characteristic : — Agriolimax lavis and Zonitoides nitidtis. 



Dominant : — Arion ater. 



' Associated with : — Agriolimax agrestis, Hyalinia crystallina, H. 

 tiitidula, H. radiatula, Z. excavatus, Euconiilus fulvus, Arion minimus, 

 A. circumscriptus, Hygromia hispida, Pyramidula rotiindata, Cochlicopa 

 lubrica, Pirostoma bideiitaia, Succinea putris, and S. elegans. 



A comparison of these two lists with that of B § i. Marsh sug- 

 gests that in some cases the water-content of the soil is the deter- 

 mining factor in the association, rather than the presence or absence 

 of lime or the particular kind of flora. 



§ 2. Ash-Oak Woodland. 



The prevailing type of woodland, indigenous and natural to the 

 Calcareous Clays, is the Ash-Oak. The summits and upper slopes of 

 the undulating hills are clothed with them, often woods of great 

 extent. They consist of large Oaks {^Qiiercus peduiiculQta~) of all ages 

 and of coppiced Ash and Ash saplings, in most cases mingled with 

 coppiced Hazel. The ground flora is rich and varied, owing to the 

 calcareous nature of the deep moist soil and comparatively abundant 

 light, for the Oaks are generally too far apart to form a dense canopy. 

 Probably the influence of the ground flora on molluscan life is inap- 

 preciable, but the abundance of moss and prevalence of fungi, upon 

 which many species actually feed, certainly affect it. All the woods 

 would be described as "damp" woods, i.e., woods with a deep soil 

 with high water-content. They are all rich in moUusca, both with 

 regard to number of species and of individuals. 



There are a few woods which show a considerable amount of Birch 

 {Beliila tomenlosa), probably planted by substitution for the natural 

 trees which have been felled. They show a similar facies of mol- 

 luscan life, though not so rich. The average Ash-Oak wood here 

 afifords the following association of species : — 



Characteristic : — Hyalinia helvetica, Azeca metikeana and Maipessa 

 laminaia. 



