Nayades.] 



MOLLUSCA. 



81 



Shell compressed, considerably elongated transversely, thin ; 

 anterior side very short; posterior side very long, and produced 

 into a somewhat lengthened, blunted beak; hinge line arcuated, 

 and ascending, its greatest altitude being nearly central; ante- 

 rior side rather narrow, and rounded; posterior side descending 

 in a waved line; basal line nearly parallel, and undulating; 

 umbones convex; outside rather smooth, and covered with a 

 blackish-brown epidermis. 



Said to be found in ponds at Liverpool, but I have never 

 met with one from that locality. 



An extremely thin and lengthened variety, which is covered 

 with a reddish-brown epidermis, and rather rough on the sur- 

 face. It inhabits Loch Kettrine, Perthshire. Our figure is 

 taken from a specimen procured in that locality. 



Variety 12. Contorta, pi. XXX, f. 7, 8. 



Shell of moderate thickness; hinge line quite parallel; the 

 ligament hardly protruding beyond the hinge line ; umbones 

 very flat ; anterior side very short, narrow, and a little point- 

 ed ; posterior side very broad, subrostrated, with a remarkable 

 flexure, caused by a strong rib-like process, emanating in both 

 valves from the umbones, and thickening towards the margin ; 

 the basal line prominently arcuated; shell considerably inflated, 

 one valve much more convex than the other. 



This remarkable variety was found by Thomas Glover, Esq., 

 of Smedley Hill, inhabiting ditches, in a flat meadow, not far 

 from the School House, at Repton, near Burton-upon-Trent. 

 Upwards of twenty specimens were obtained by him. Sir 

 Oswald Mosley kindly undertook to procure specimens of this 

 desirable shell; but on visiting the spot, found the locality com- 

 pletely destroyed, in consequence of a new bridge having lately 

 been built across the Trent ; and although the ditch in which 

 they were found communicated with the river, yet no traces of 

 the shell could be found. 



Genus 2 — Unio — Bruguiere. 



Shell transverse, equivalve, inequilateral, free, sometimes sub- 

 cordate, or suborbicular; pearlaceous within; generally covered 

 with a dark olivaceous epidermis, which is usually decorticated 

 on the umbones; hinge provided with a short, irregular, simple, 

 or a double compound tooth, which is almost always striated ; 

 with two elongated, compressed, lateral teeth, the front one 

 produced, sometimes obsolete; two muscular impressions in 

 each valve, the superior one compound, or composed of several 

 divisions ; ligament external. 



1. Unio pictorum, pi. XXXI, f. 7, 8, 9, 10, 11. 



Unio pictorum, First Ed., pi. 26, f. 4 ; Lamarck, An. San. 

 Vert., VI, p. 77; Ency. Meth., pi. 248, f. 4; Pfeiffer, I, p. 115, 

 pi. 5, f. 9, 10; Drapernaud, Moll., pi. 11, f. 4; Rossmassler, 

 I, pi. 3, f. 71, a, b; lb., Ill, p. 23, pi. 13, f. 197 ; lb., IX and 

 X, p. 10, pi. 45, f. 587 to 590; Unio rostratus, Pfeiffer, I, p. 

 114, pi. 5, f. 8 ; Mya pictorum, Sturm, Fauna, VI, p. 2, f. a; 

 Schroeter, Flussconch., pi. 4, f . 6 ; Wood, Conch., p. 104, pi. 

 19, f. 3, 4 ; Donovan, Brit. Sh., Ill, pi. 89; Mya ovalis, Mon- 

 tagu, Test. Brit., p. 34; Mysca pictorum, Turton, Man., p. 20, 

 pi. 2, f. 1 1 ; Gray's Turton, p. 295, pi. 2, f. 1 1, badly figured. 



Shell thin, transversely oblong-oval, ventricose ; umbones a 

 little produced, and placed near to the anterior side, which is 

 short, and rounded; posterior side elongated, and somewhat 



pointed; hinge line slightly bent; basal line nearly parallel, and 

 a little hollowed in the centre ; hinge furnished with a strong, 

 double, compressed, elevated, elongated, crested, crenated, car- 

 dinal tooth in the left valve, with a perpendicularly papillose, 

 striated cleft on the side of its posterior portion, on which the 

 tooth of the opposite valve rests, which locks into a space above 

 the shorter cardinal tooth in the opposite valve; lateral teeth in 

 both valves long, narrow, and sunk at the umbones, — from 

 whence they take their rise, — becoming more elevated and 

 acute as they diverge, and extend the same length as the liga- 

 ment; inside highly pearlaceous; varying in different specimens 

 from bluish-white to a rich salmon-colour, with faint, nearly 

 obsolete radiations, extending from the umbones to the mar- 

 gins; pallial impressions well marked; anterior muscular im- 

 pressions very deep; posterior ones distinctly defined ; outside 

 covered with a smooth, shining, yellowish-green epidermis, but 

 varying in colour from different localities; with very indistinct, 

 nearly obsolete, divergent grooves, radiating from the umbones 

 to the margins; and with transverse, concentric, slight furrows, 

 and very irregular, transverse striae, most conspicuous towards 

 the sides. 



Fig. 11, pi. XXXI, is an external view of the teeth of the 

 hinge. 



Found in the river Ouse, at York; the Aire, near Gargrew: 

 the Severn, near Shrewsbury ; in the Aire, near Skipton ; the 

 Avon, near Leamington, Warwickshire; and several other slow 

 running rivers and lakes in Britain. 



Variety 1, pi. XXXI, f. 7 and 10. 



Rossmassler, III, p. 23, pi. 13, f. 196; lb., I, p. 118, pi. 3. 

 f. 71, a, b. 



The length somewhat more than two-fifths of its breadth ; 

 thickness a third more than its length. This is the ordinary 

 form of the species. 



Found in the Ouse, at York; the Severn, near Shrewsbury: 

 the canal, near Birmingham ; and Sir Oswald Mosley, Bart., 

 sent me some beautiful specimens, from the lake at Rolleston. 

 with the insides of a rich nacred, pale salmon-colour. In this 

 locality they grow to a very large size, measuring an inch 

 and three-quarters in length, and upwards of four inches in 

 breadth. 



Variety 2, pi. XXXI, f. 8. 



Rossmassler, I, p. 1 1 7, pi. 3, f. 70, a, Unio tumidius. 



The posterior side more pointed, that side gradually dimi- 

 nishing both above and below, from the umbones. Length 

 five-tenths of its breadth ; thickness half its length ; cardinal 

 and lateral teeth longer and more prominent than in the first 

 variety. 



Inhabits the Aire, near Gargrew ; and the river Brothav. 

 which empties itself into Windermere, near Ambleside. 



Variety 3, pi. XXXI, f. 9- 



Considerably longer than the former two varieties, being 

 nearly a third, in proportion to its breadth ; the umbones more 

 central and prominent ; and somewhat more inflated. 



Found in the Don, at Sheffield. 



2. Unio Deshaysii, pi. XXXII, f. 1, 2, 3, 4. 



Unio Deshaysii, Rossmassler, III, p. 23, pi. 13, f. 197; Gib- 

 son, MSS. 



Shell thickish, much elongated transversely; hinge line slighth 

 curved; basal line nearly parallel, slightly waved in the centre. 



