ANCYLUS. 4] 
Genus IV.—ANCYLUS. 
1. A. FLUVIATILIS (inhabiting rivers). 
Much the shape of the common marine limpet; apew re- 
_-~ eurved, giving the name Ancylus (little hook) to the genus. 
Found very commonly adhering to stones or wooden 
piles in streams, but not in still water. It is common 
throughout Great Britain and Ireland, but is not found 
further north than Aberdeenshire. 
Var. I. capuloides. Larger and higher. 
Var. II. gibbosa. Smaller, with the hook over- 
hanging the posterior margin. 
Var. III. albida. White, more finely striated. 
2. A. LACUSTRIS (inhabiting ponds). 
Compressed, oblong, thin; apex acute, interior often 
iridescent. 
Found in sluggish streams, canals, ponds, &c., on 
the stalks of many aquatic plants, especially the 
Stratiotes and rushes. It is more local than the last 
species, but is abundant where it occurs. Its com- 
pressed, oblong shape marks it off distinctly from A. 
fluviatilis. 
Var. I. compressa. Broader and flatter. 
Var. II. albida. Milk white. 
