NAYADES. 115 



Variety 3. Minor, pi. XXIII, f. 2. 



Unio margaritifera, minor, Rossmassler, II, p. 21, pi. 9, f. 

 129; Nat Michaud; Alasmodon minor, Brown, Illust. Conch., 

 p. 83, pi. 30,* f. 2. 



Shell small, subcompressed ; valves very thick ; the cardinal 

 teeth compressed, and small; general form like variety 1. Sel- 

 dom exceeding an inch and a half in length ; and three inches 

 and a half in breadth. 



Inhabits the Mint, near Kendal. 



Rossmassler is wrong in supposing that this variety belongs 

 to the form Roissyi. 



I am indebted to the kindness of Miss Ellen T. Thomson, 

 of Stricklandgate, and Thomas Gough, Esq., surgeon, Kendal, 

 for specimens and a knowledge of this variety. 



Variety 4. Arcuata, pi. XXIII, f. 3. 



Alasmodon arcuata, Brown, Illust. Conch., p. 84, pi. 30,* 

 f. 3. 



Shell small, subdepressed, thick; hinge line considerably 

 arcuated ; ligament prominent ; basal line greatly curved ; car- 

 dinal tooth in one valve very large ; lateral sinus arcuated, and 

 broad as it retires from the cardinal tooth ; muscular impressions 

 deep. 



Found in the river Derwent, Bassenthwaite, Cumberland, a 

 little way below Ouse Bridge. 



Variety 5. Olivacea, pi. XXIII, f. 1. 



Alasmodon olivacea. Brown, Illust. Conch., p. 84, pi. 30,* 

 f. ]. 



Small; substance of the shell thick, rather inflated; hinge line 

 nearly parallel ; basal line with a flexure, and a very little arcu- 

 ated; valves with a slightly hollowed, longitudinal, gradually 

 widening furrow, from the umbones to the basal margin ; outer 

 surface olivaceous, with irregular, transverse furrows ; umbones 

 much decorticated, which extends nearly to the dorsal extre- 

 mity of the valves ; inside of a dull flesh-colour, slightly nacred 

 towards the dorsal side ; teeth small, distinctly tripartite in the 

 left valve, and very small and single in the other. 



This very curious variety was discovered by Thomas Glover, 

 Esq., of Smedley Hill, in the Leven, a little way below the lake 

 of Windermere, Westmoreland, where it appears to be the pre- 

 vailing form. 



