II.—MOLLUSCA.
The district around Birmingham is an excellent field for terrestrial and fluviatile Mollusca. Within a circle of twelve miles radius, which includes a portion of the Counties of Warwick, Stafford, and Worcester, can be found fifty per cent. of the species and varieties enumerated in Dr. J. Gwyn Jeffreys’ “British Conchology.” No special quality of soil or geological condition is required for the existence of Molluscs; whatever the nature of the ground may be, some species or other will reward the searcher. The number of terrestrial species is usually the greatest where limestone is present; indeed some species do not seem able to maintain their existence away from it, e.g., Helix ericetorum, H. virgata, H. arbustorum, and Cyclostoma elegans. The still beautiful grounds of Dudley Castle were once “happy hunting grounds” for the collectors of Mollusca, but the smoke of a thousand fires has cast a baleful influence over the locality. The dead shells of species, once abundant, are conclusive evidence that the Molluscan fauna do not now enjoy a congenial atmosphere in that neighbourhood. Helix arbustorum, may, notwithstanding, still be found there, its nearest proximity to Birmingham.
Among the noticeable species of the district may be mentioned Testacella Haliotidea, found in the garden of a florist at Redditch; Succinea virescens, (Morelet) = S. putris var. vitrea (Jeffreys), which the writer has taken near Plants Brook Reservoir; Zonites glaber, found near Solihull; Helix Cantiana,[62] Henley-in-Arden; H. virgata, Grafton, near Alcester; Balia perversa, Fenny Compton, Northamptonshire. The three last named species are outside the twelve miles radius.
Conchifera.
The Midlands are rich in fluviatile forms, nearly all the known British species occur. Those worth noting among the Sphæriidæ are—Sphærium corneum, var. Scaldiana, Acock’s Green; S. corneum, var. flavescens, Plants Brook; S. rivicola and S. ovale, Acock’s Green and Rushall Canal. S. lacustre is not uncommon, and is found abundantly in a pond at Handsworth.
The Pisidia are well represented, four out of our five species occurring. It is curious that the large form Pisidium amnicum has not hitherto been taken in the district. The writer took P. roseum[63] from several ponds at Meriden in 1885-6.
The Unionidæ are extremely plentiful, and the two species Unio tumidus and U. pictorum attain to an immense size. In the writer’s cabinet are examples of U. pictorum of the following dimensions—2¹⁄₁₆ in. × 5¹⁄₁₆, 2¹⁄₁₆ in. × 5¼, 2³⁄₁₆ in. × 5¼, some of them weighing nearly 4 ounces avoirdupois; and of U. tumidus, 2⁵⁄₁₆ in. × 4¾, 2⅜ in. × 4⅞, 2¾ in. × 5, the weight of some examples reaching nearly 6 ounces avoirdupois. These are probably the finest shells of their kind ever taken anywhere. Anodonta cygnea is common, and its varieties incrassata, Zellensis, pallida, and rostrata occur. A. anatina, and the varieties radiata and ventricosa are found; handsome shells of the latter occur at Barr Park and in the river Blythe at Coleshill. Dreissena polymorpha is commonly distributed.
Gasteropoda.
In the order Pectinibranchiata, Neritina fluviatilis, the only representative in England of a genus of world-wide distribution, has occurred in the river Tame at Aston, but the writer believes is not now to be found there. One of our two species of Paludinidæ, Paludina vivipara,[64] Bythinia tentaculata, B. Leachii, and Valvata piscinalis make up the list of operculate water snails.
Among the Limnæidæ examples of the following genera occur. In the genus Planorbis we find all the species except Planorbis lineatus, excluding of course P. dilatatus (Gould), which only occurs at Manchester, having been introduced on cotton from America. The epiphragm formed by P. spirorbis, in summer, when the solar heat has dried up its habitat, is a singular item of its economy. It is supposed that this habit enabled P. dilatatus to reach our shores. Physa hypnorum and P. fontinalis are both represented; they are charming inhabitants of an aquarium, their habit of thread spinning,[65] especially in the young state, makes them lively creatures; the lobed mantle of P. fontinalis, nearly enclosing the shell, gives a peculiar character to the animal.