The mere inspection of this table will show that most of the species have a very extensive range, having been found in all parts of our island where there has been a zoologist who has taken any interest in searching for them. Thus we find, that out of the 128 species recorded in this work, 107 species are found within a circle of about 15 miles of the metropolis, and 89 in the northern district of England. Of the species which are confined to the southern half of the kingdom there may be noticed among the aquatic kinds Assiminia Grayana, only found in the Thames and the streams running into it, from its mouth to where the water is only slightly brackish, or nearly fresh, at the very highest tides, as at Greenwich, for example. Paludina vivipara and P. achatina are not found in the northern part of the island. P. crystallina is found in the rivers of Cambridgeshire, Oxfordshire, Essex, and Suffolk; and P. achatina is very common in the Thames, and also in the rivers of some of the before-mentioned counties: they are found together in the river Colne, at Uxbridge. These species avoid the slightest degree of brackishness in the water, and are therefore only found in the upper part of the rivers. Bithinia ventricosa is very commonly found with this latter in the Thames, and in Suffolk; but it keeps in the smaller streamlets, and is not so particular about the absence of brackishness, for it is found with B. impura and Assiminia in the streams of the Greenwich marshes. Neritina fluviatilis, and Planorbis corneus, are also confined, as far as I have had the opportunity of learning, to the southern part of the island. Montagu says that Dorsetshire is the western limit of the Neritina; this is curious, as it and the two species of Paludina are found in Ireland. Segmentina lineata has only been mentioned as found near London and in the south-west of England. Near London it is not uncommon. Limnæus acutus (if it is more than a variety of L. pereger) has only been recorded as found in South Wales. Cyclas rivicola is almost peculiar to the Thames : its northern limit is, I believe, the Trent in Nottinghamshire: it is also found in Germany. Pisidium obtusale, P. nitidum, and P. Henslowianum, have only been recorded as found near London, in Surrey, and in Cambridgeshire; but this, perhaps, is because they have not been searched for elsewhere. The Uniones (U. pictorum, U. tumidus, and U. Batavus) are not recorded as being found in the north of England, or in Scotland, as far as I know. Among the southern terrestrial species, Testacella haliotoidea seems confined to the gardens in the neighbourhood of London, Plymouth, Biddeford, and to the island of Guernsey. Helix obvoluta, to the chalk downs of Hampshire. This species is common to the north of France and Germany. Helix limbata has only been found in the hedges near Hampstead, Middlesex; but it is very doubtful if these specimens had not been introduced: it is common in the southern part of France, and has been found as far north as Caen. |