108 NAYADES. 



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

 Avon, near Leamington, Warwickshire; and several other slow 

 running rivers and lakes in Britain. 

 Fariety 1, pi. XIX, f. 1 and 4. 



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

 f. 71, a, b; Brown, Illust. Conch., p. 81, pi. 31, f. 7 and 10. 



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 RoUeston, 

 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. 



raiiety 2, pi. XIX, f. 3. 



Rossmassler, I, p. 117, ph 3, f. 70, a,Unio tumidius ; Brown, 

 Illust. Conch., p. 81, pi. 31, f. 8. 



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 Brothay, 

 which empties itself into Windermere, near Ambleside. 

 Variety 3, pi. XIX, f. 2. 

 Brown, Illust. Conch., p. 81, pi. 31, 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. XX, f. 3, 4. 

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

 son, MSS.; Brown, Illust. Conch., p. 81, pL 32, f. 1, 2, 3, 4. 



Shell thickish, much elongated transversely; hinge line slightly 

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

 ascending rather abruptly towards the posterior side, and form- 

 ing a subrostrated termination ; umbones prominent, placed 

 very near the anterior side, which is short, and rounded ; pos- 



