154 SPHAERIIDE. 
Var. IV. pisidtoides (Gray). Somewhat triangular, 
strie coarser than in the type. 
2. §S. R{vIcoLa (tnxhabitant of streams) Leach. V1. IX., f. 2. 
Oval, solid, opaque, glossy, greenish or yellow when young, darker 
when adult; s¢72@ evenly concentric; /¢gament short but conspicuous ; 
scars distinct; ¢e¢h as in the last species but larger. L. 175 mm. 
B. 224 mm. 
This is the largest species of the genus. It is much 
flatter than .S. corneum, especially when young ; more solid 
and more strongly striated. 
It inhabits canals and slow rivers in various parts of 
England. It is said to have been taken in Dublin, but it 
has not been recorded for Wales or Scotland. 
Var. flavéscens (Moq.). 
3. S. PALLIDUM (fale) Gray. Pi. IX., f. 3. 
[=S. ovALE Jeffreys. ] 
Oblong ; shoulders sharp ; thin, semi-transparent, dull, pale grey ; 
strie faint, concentric ; deaks nearly central; /7gament long ; hinge 
straight on posterior, incurved on anterior side ; ¢eeth small; scars 
distinct. L. 10mm. B. 15 mm. 
This is a local species, found in canals and ponds in 
Lancashire, Yorkshire, Warwickshire, Staffordshire, Surrey, 
and Middlesex, but not in Ireland, Wales, or Scotland. 
It is probably of recent introduction, and was only 
noticed about 1824, though a single valve has been found 
in the fossiliferous alluvial deposit near London. 
