106 NAYADES. 



umboues convex ; outside rather sniootli, 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, whicli 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. XVIII, f. 1, 2. 



Anodon contorta, Brown, Illust. Conch., p. 81, pi. 30, 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 II. — UNIO Bruguicre. 



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. 



