ST. ALBANS AND ITS NEIGHBOURHOOD. 
233 
within a radius of five miles from the centre of the city lies upon 
the Chalk, a formation peculiarly suited to the needs of many 
land Mollusca. The calcareous nature of the soil implies 
a deficiency in surface-water, and ponds and marshes are few. 
This deficiency is to some extent remedied by the Ver and Colne, 
which traverse the district, and the Lea, which skirts it for 
a short distance in the north-east. These rivers flow through 
low-lying meadow-land, and the ditches and water-cress beds 
associated with them provide congenial quarters for many fresh¬ 
water forms. The Grand Junction Canal, which passes just 
beyond the western boundary, is the habitat of several species, 
including Neritina fluviatilis, JJnio pictorum, U. tumidus, 
Sphserium rivicolct, and Pisidium supinum, which have not been 
recorded for the district, whilst Paludestrina jenkinsi, a notable 
colonist, which abounds in the Colne at Watford, has probably 
ere this invaded our area. No systematic investigation of the 
Mollusca of St. Albans has apparently ever been made, and the 
paucity of our information is no measure of the actual fauna; 
all or nearly all of the land molluscs known to occur in Hertford¬ 
shire will probably be found eventually in the district. 
Arion ater is plentiful, perhaps the commonest form being the 
var. oculata, whilst the vars. succinea, brunnea, and plumbeci also 
occur. Limax maximus, L. arborum, Arion subfuscus, A. inter¬ 
medins, A. hortensis, and A. circumscriptus are common in woods 
in autumn, and Limax tenellus occurs in Prse Wood. Agriolimax 
agrestis is a common pest, but its congener A. Isevis is local. 
The type and the var. maculata occur in the meadows of the 
Colne near Park Street. 
Hyalinia helvetica is the commonest member of its genus. 
H. nitidula, ii . alliaria, H. cellaria, H. pura, and // crystallina 
are generally distributed. PL. radiatula has been found in Prae 
Wood and at Aldenham, and H. nitida in the meadows near 
Park Street. 
Euconulus fulvus, sometimes abundant in rushy places, is 
found too, although more sparingly, in woods, where it is often 
associated with Vitrina. pellucida. Punctum pygmseum has been 
taken near St. Albans, and is probably not uncommon in suitable 
situations elsewhere. Sphyradium edentulum occurs sparingly 
in Pi'88 Wood. Pyramidula rotundata is ubiquitous. Enaobscura , 
Clausilia laminata, and C. bidentata are fairly common in woods 
and copses, whilst Carychium minimum abounds in such places. 
Cochlicopa lubrica is general, but Azeca tridens is local. It has 
been found at St. Albans and Sandridge, the var. crystallina 
being associated with the type at the latter place. Pomatias 
elegans may be found in hedgerows and about old chalk-pits 
at Wheathampstead, Gorhambury, and Munden. Jaminia 
muscorum and J. cylindracea are sparingly distributed, whilst 
Vertigo antivertigo has been taken in rushy places in the Colne 
Valley near Munden. Succinea elegans and S. putris occur 
among rushes and coarse vegetation in wet places. 
