94 MOLLUSCA. 
Found in most water streams, and in stagnant ditches and 
pools, throughout Britain and Ireland; is common in Dudding- 
ston Loch, near Edinburgh, of the size above described, which 
is considerably more than its ordinary dimensions. 
This shell is readily distinguished from the C. rivicola, by its 
more ventricose shape, in being thinner, more transparent, and 
seldom measuring above half the size of the former. 
3. CycLas Lacustris, pl. XXXIX, f. 20. 
Cyclas lacustris, First Ed., pl. 17, f. 16; Drapernaud, Hist. 
des Moll., p. 130, pl. 10, f. 6, 75 Lamarck, V, p. 559, No. 3; 
Turton, Man., p. 14, f. 4; Pfeiffer, p. 122, pl. 5, f. 6,7; Fle- 
ming, Brit. An., p. 453. 
Shell thin, rhombic-orbicular, subequilateral, somewhat com- 
pressed; sides rather obtuse, rendering the general contour 
more circular than others of the genus; obsoletely striate ; 
beaks obtuse, of a grayish ash-colour. 
Found in Ulliswater; a small pond on the grounds at Corby, 
Cumberland ; and at Prestwick Car, Northumberland. It is a 
rare British shell. 
It is much more compressed than any of the other British 
Cyclyde. 
4. Cycuas caLycuLata, pl. XXXIX, f. 21. 
Cyclas calyculata, First Ed., pl. 17, f. 13; Drapernaud, Hist. 
des Moll., p. 130, pl. 10, f. 14, 15; Lamarck, V, p. 559, No. 55 
Pfeiffer, p. 122, pl. 5, f. 17, 18; Turton, Man., p. 14, f. 35 
Forbes, p. 50; Cyclas lacustris, Alder, Mag. Zool. and Bot., I, 
p- 118. 
Shell thin, rhombic-orbicular, grayish ash-coloured, com- 
pressed, diaphanous, substriate, or nearly smooth; slightly 
angular on one side; umbones very prominent, and acute. 
About a quarter of an inch long; and its width nearly the 
same. 
Found in the lakes of Westmoreland, and is not uncommon 
in several pits and ponds near Manchester, but is a very rare 
and local species. 
Genus 16.—Pisip1umM.—Pfeiffer. 
Shell equivalve, transverse; sides unequal, completely closing ; 
in the right valve one, and in the left valve two opposite, very 
small, primary teeth; behind and before, two thin, lamellar, side 
teeth; those of the latter cleft in the right valve, in order to 
receive the opposite ones. 
The shells of this genus are distinguished from those of 
Cyclas, by being less equilateral in their form, and in the liga- 
mentary side being shortest, which is the reverse in Cyclas. 
1. Pistp1uM oBLiquum, pl. XXXIX, f. 22. 
Pisidium obliquum, First Ed., pl. 17, f. 14; Cyclas obliqua, 
Lamarck, V, p. 559, No. 4; Pisidium obliquum, Pfeiffer, p. 
124, pl. 5, #19, 20; Cyclas palustris, Drapernaud, Hist. des 
Moll., p. 131, pl. 10, f..17, 18; Cyclas amnica, Turton, Brit. 
Biy., p- 250, pl. 11, f. 15; Ib., Man., p. 15, f. 53 Cyclas amni- 
cus, Fleming, Brit. An., p. 453; Tellina amnica, Gmelin’s 
Linné, I, p. 3242, No. 78; Miiller, p. 205, No. 389; Tellina 
rivalis, Linn. Trans., IV, p. 187; Donovan, Brit. Sh., II, pl. 
64, f.2; Cardium amnicum, Montagu, p. 86. 
[Concuacka. 
Shell thin, subpellucid, of a brownish or grayish horn-colour, 
obliquely oval, moderately convex, and sulcated concentrically, 
with the furrows finely striated; beaks tumid, a little produced, 
and placed considerably towards the anterior side; left valve 
provided with a double central tooth, and two lateral teeth on 
each side, standing parallel one within the other, the outer of 
which is very small; right valve with two cardinal, appoximating, 
oblique teeth, with one lateral tooth on each side, that on the 
posterior side strong, and elevated above the margin of the 
shell; inside bluish-white, dim in the disk, but glossy towards 
the margin; on each side are distinctly visible, large, smooth 
spaces, to which the muscles adhere. Length three-eighths of 
an inch; breadth half an inch: although it is but rarely met 
with of this size. 
Found in slow running rivers and streams, and is known to 
inhabit the Avon, Wiltshire; in the water-courses in the mea- 
dows near Wareham, Dorsetshire; the Liffey, Ireland, near 
Sallins, Kildare, and in rivulets which run through the bog at 
that place; we have also met with it in a stream, which empties 
itself into the Water of Leith, a little way above Colt Bridge, 
near Edinburgh; and many other localities. 
2. PiIsIDIUM FONTINALE, pl. XXXIX, f. 23. 
Pisidium fontinale, Pfeiffer, Land un Was. Sn., p. 126, pl. 
5, f. 15, 16; Brown, Edin. Journ. Nat. and Geo. Science, I, 
p- 11 and 413, pl. 1, f. 5, 6, 7; Cyclas fontinalis, Drapernaud, 
Hist. des Moll., p. 130, pl. 10, f. 11, 12; Lamarck, An. San. 
Vert., V, p. 559, No. 7; Cyclas pusilla, Turton, Conch. Dict.; 
Ib., Brit. Biv., p. 251, pl. 11, f. 16, 17; Ib., Man., p. 16, f. 7; 
Pisidium pulchellum, Jenyns, Monog., p. 18, pl. 21, f 13 
Thompson, Ann. and Mag. Nat. Hist., VI, p. 53; Forbes, 
Mal. Mon., p. 50. 
Shell suboval, oblique, very convex, pellucid, and covered 
with extremely fine, concentric, rather obscure striz ; umbones 
obtuse, placed nearest the anterior side; hinge with one central 
and two lateral teeth in the right valve, and two oblique car- 
dinal and one lateral tooth in the other; colour pale ash. A 
little more than an eighth of an inch in length; and somewhat 
more in breadth. 
First discovered in a ditch at Duddingston Loch, near Edin- 
burgh, by my friend James Gerard, Esq. I have since found it 
in the ditch at the north end of the Loch, and also in a ditch 
at Hunter’s Bog, King’s Park. 
Turton, in his Manuel, says it is found “in most streams and 
brooks,” but although I have examined numerous localities in 
England, Ireland, and Scotland, I have not found it so common 
as he alleges. 
3. Pisip1uM oBTusALE, pl. XXXIX, f. 24. 
Pisidium obtusale, Alder, Mag. Zool. and Bot., IU, p. 118; 
Pfeiffer, p. 125, pl. 5, f. 21, 22; Brown, Edin. Journ. Nat. and 
Geo. Science, I, p.413; Thompson, Ann. and Mag. Nat. Hist., 
VI, p. 533 Cyclas obtusalis, Lamarck, V, p. 559, No.6; Pera 
gibba, Leach, MSS. 
Shell oblique, ventricose, heart-shaped; sides somewhat une- 
qual; beaks prominent, and obtusely rounded; pellucid, yel- 
lowish-white, or pale horn-coloured; with extremely minute, 
concentric, thin strie; the lower edges of the valves rather 
sharp. Length an eighth of an inch; breadth an eighth and a 
quarter ; thickness not quite an eighth. 

