SWANTON: THE MOLLUSCA OF WILTSHIRE. I3I 



In addition to the three collections above alluded to, I have also 

 examined one formed by Mr. C. D. Heginbothom, who has been an 

 assiduous collector for many years in the neighbourhood of Devizes. 

 I am specially indebted to him for much kind help in the preparation 

 of these notes ; also to my friend, Mr. Thomas Baker, of Salisbury, 

 the well-known Wiltshire antiquary. 



Sources from which information has been obtained, additional to 

 those already indicated, are given in the Bibliography at the end of 

 this paper. 



The greatest length and breadth of Wiltshire are respectively fifty- 

 four and thirty-seven miles. Its area is i:354 square miles or 866,677 

 acres. The population, as might be expected in a county containing 

 so much open pasture land, is remarkably small, being (in 1901) 

 only 273,845. The soil is chiefly chalk. A Greensand valley divides 

 the Marlborough Downs from the great Salisbury Plain, and both are 

 bounded by Greensand on the west. Roughly speaking, a belt of 

 Greensand stretches across the county from the neighbourhood of 

 Swindon in the north-east to Warminster in the west, and separates 

 the north-western third, containing the Oolites, from the Chalk, which 

 chiefly constitutes the remainder. The Oolites are also exposed in a 

 triangular area in the south-west around Mere and Tisbury. Tertiary 

 strata occur in patches near Bedwyn and Savernake in the north-east, 

 south-east of Salisbury (around West Grinstead), and in the extreme 

 south near Cranborne. There are Quaternary Gravels in the Avon 

 Valley near Salisbury. The county is well watered; the Kennet flows 

 through the Marlborough Plain to join the Thames at Reading ; the 

 Somerset Avon drains the Oolites of the north-west, whilst the Hamp- 

 shire Avon passes from north to south through Salisbury Plain, from 

 near Devizes to Salisbury, where it is joined by its tributaries, the 

 Wyly and Nadder (uniting at Wilton), from the south-west. 



The Avon and Kennet Canal forms the separating line between the 

 two vice-counties. It enters the county at Hungerford, bending to 

 the south-west to Pewsey Vale (Greensand) through which it winds a 

 westerly course to Devizes. West of this town it is cut through the 

 Oolites, passing successively over Portland Beds, Oxford Clay, and 

 Cornbrash, joining the Avon a few miles south of Bradford on the 

 western border of the county. 



One-hundred-and-eleven species have been observed. Four of 

 these are new records : — -Agriolwiax lavis, Milax sowerbyi, and Val- 

 lonia excentrka have been added by the writer ; Planoibis glaber was 

 found by Mr. F. Townsend at or near Great Bedwyn more than half- 

 a-century ago, but its occurrence there has not been previously 

 published. 



