242 lOURNAI. OK CONCHOI.OOY, VOL. l6, NO. 7, SEI'TEMTiKK, I92I. 



A. liter here shows a great range of variation, numerous examples 

 occurring of the following varieties : — rufa, brunnea, plu/nbea, swain- 

 merdami^ castanea, Viwdfasciata. H. nemoralis abounds, but exhibits 

 remarkably little variation, the shells being of but average size, with 

 heavily-banded specimens predominating. 



§ 2. Non-Calcareous Pasture. 



Subject to the same reservation with regard to Scrub, as in the case 

 of Calcareous Pasture, the alluvial flats of the valley of the Nene 

 afford examples of non-calcareous pasture, the soil overlying great 

 beds of river gravel. 



Dominant : — Arioii ater \ associated with Agriolimax agrestis, 

 Hyalmia nitidula, Theba cantiana, Hygromia hispida, If. siriolata, 

 Vallonia costata, Helicigona arbustorjiin, Helix aspersa., H. nemoralis., 

 H. hortensis, and Cochlicopa hibrica. 



Perhaps the characteristic species of this type of habitat is H. arbus- 

 tornin, which is certainly dominant over the other members of the 

 Helicidce, especially when the pasture is becoming Scrub. Also where 

 these pastures adjoin woods, many woodland species appear in the 

 association, e.g., V. pellucida, H. helvetica., H. cellaria, P. rotutidata, 

 E. obscura, and P. bide?itata, but it seems advisable to omit them 

 from the Grassland lists and place them in their true positions. 



Snb-section : Subterranean. 

 Ccecilioides acicnla universally and abundantly distributed on both 

 types of pasture ; probably an isolated species. 



B.— Wet Grasslands. 



§ I. Marsh. 



The mollusca of the marshy margins of rivers and ponds are 

 included under these respectively. The following association is that 

 of a typical natural marsh, an extensive tract of boggy ground, marked 

 by the presence of the Common Rush, Cotton Grass, Bog Bean, 

 jNIarestail, and Peppermint. 



Characteristic : — Zonitoides nitidus and Vertigo antivertigo. 



Associated with : — Agriolimax Icevis, Hyalinia radiatnla, Enconuhis 

 fulviis, Ario7i ater, A. minimus., Hygro7nia hispida, Cochlicopa lubrica, 

 Succinea elegans, Carychium minimum., Pisidium casertamim, and P. 

 personatum, 



V. antivertigo is found in the dampest moss among the rushes, 

 while E. fulvus'xs, extremely plentiful and of the small, strongly-striated 

 var. alderi. 



§ 2. Hard- JVater Ponds. 



Situated on a highly calcareous soil and fed by hard-water springs, 

 the great majority of the ponds are of this type. They are very 



