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middle of the back edge. The first species of this 

 genus is Spharium cor mum ; it has ,a sub-globular 

 shell, nearly equilateral, it is glossy, of a horn colour, 

 often with paler bands, which indicate periods of 

 growth, sometimes with rays of faint brown from the 

 beaks to the front edge, with indistinct longitudinal 

 lines, under a magnifying glass appearing reticulated. 

 The epidermis is thin, the beaks central, the ligament 

 short, a strong hinge with a double cardinal tooth in 

 each valve, two lateral teeth in the right and four in the 

 left valve. The inside of the shell is bluish-white. 

 The length is 0-35, the breadth 0*45. There are several 

 varieties ; one is of a straw colour, and 

 is smaller and rounder. One, again, 

 is more oval, and paler in colour. 

 Another has the shell sub-triangular, 

 with transverse striae. It inhabits slow 

 rivers, ponds, and ditches throughout 

 the country. S. rivicolum, the second 

 species, may be distinguished from S. corneum by 

 its greater size, the length being 07, breadth 0-9, 

 and oval shape; the ligament is very r conspicuous, and 

 the ridges on the shell are strong. It inhabits the 

 same localities. 



S. ovale, the third species, has the shell oblong, 

 compressed less equilateral than the preceding ; it 

 is thin and semi-transparent, yellowish, with some- 

 times a darker tint, and zones of growth, occasion- 

 ally some faint rays, towards the margin fine con- 

 centric lines, the anterior side rounded, the posterior 

 truncate sloping to the margin, which is curved and 

 sharp, the beaks are small, the ligament long and 

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