94 



MOLLUSCA. 



[Conch acea. 



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, pi. XXXIX, f. 20. 



Cyclas lacustris, First Ed., pi. 17, f. 16 ; Drapernaud, Hist, 

 des Moll., p. 130, pi. 10, f. 6, 7 ; Lamarck, V, p. 559, No. 3 ; 

 Turton, Man., p. 14, f. 4 ; Pfeiffer, p. 122, pi. 5, f. G, 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 UUiswater; 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 

 Cyclydae. 



4. Cyclas calyculata, pi. XXXIX, f. 21. 



Cyclas calyculata, First Ed., pi. 17, f. 13; Drapernaud, Hist, 

 des Moll., p. 130, pi. 10, f. 14, 15; Lamarck, V, p. 559, No.5; 

 Pfeiffer, p. 122, pi. 5, f. 17, 18; Turton, Man., p. 14, f. 3; 

 Forbes, p. 50; Cyclas lacustris, Alder, Mag. Zool. and Bot., II, 

 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 Pisidium 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. Pisidium oblicjuum, pi. XXXIX, f. 22. 



Pisidium obliijuum, First Ed., pi. 17, f. 14; Cyclas obliqua, 

 Lamarck, V, p. 559, No. 4 ; Pisidium obliquum, Pfeiffer, p. 

 124, pi. 5, f. 19, 20; Cyclas palustris, 'Drapernaud, Hist, des 

 Moll., p. 131, pi. 10, f. 17, 18; Cyclas amnica, Turton, Brit. 

 Biv., p. 250, pi. 1 1, f. 15 ; lb., Man., p. 15, f. 5 ; Cyclas amni- 

 cus, Fleming, Brit. An., p. 453 ; Tcllina amnica, Gmelin's 

 Linne, I, p. 3242, No. 78 ; Midler, p. 205, No. 389 ; Tellina 

 rivalis, Linn. Trans., IV, p. 187; Donovan, Brit. Sh., II, pi. 

 64, f. 2 ; Cardium amnicum, Montagu, p. 86. 



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. Pisidium fontinale, pi. XXXIX, f. 23. 



Pisidium fontinale, Pfeiffer, Land un Was. Sn., p. 126, pi. 

 5, f. 15, 16; Brown, Edin. Journ. Nat. and Geo. Science, I, 

 p. 11 and 413, pi. 1, f. 5, 6, 7 ; Cyclas fontinalis, Drapernaud, 

 Hist, des Moll., p. 130, pi. 10, f. 11, 12; Lamarck, An. San. 

 Vert., V, p. 559, No. 7; Cyclas pusilla, Turton, Conch. Diet.; 

 lb., Brit. Biv., p. 251, pi. 11, f. 16, 17; lb., Man., p. 16, f. 7 ; 

 Pisidium pulchellum, Jenyns, Monog., p. 18, pi. 21, f . 1 ; 

 Thompson, Ann. and Mag. Nat. Hist., VI, p. 53 ; Forbes, 

 Mai. Mon., p. 50. 



Shell suboval, oblique, very convex, pellucid, and covered 

 with extremely fine, concentric, rather obscure stria?; 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. Pisidium obtusale, pi. XXXIX, f. 24. 



Pisidium obtusalc; Alder, Mag. Zool. and Bot., II, p. 118; 

 Pfeiffer, p. 125, pi. 5, f. 21, 22; Brown, Edin. Journ. Nat. and 

 Geo. Science, I, p. 413; Thompson, Ann. and Mag. Nat. Hist., 

 VI, p. 53 ; Cyclas obtusalis, Lamarck, V, p. 559, No. 6 ; P era 

 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 stria; ; 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. 



