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. Of the six species of Limnæa[66] which occur, it will not be needful to mention more than one, which is the rarest with us, viz.: _Limnæa glabra_. Both species of Ancylus are moderately common.