PLANORBIS. MAL 
Sub-genus.—GYRORBIS Agassés. 
6. BP. SPIRORBIS (czrcular coil) Miller. Pl. VI., f. 6. 
Very flat, rather solid, glossy, brown horn-colour ; whorls 5 to 6; 
faintly carinated on the lower margin. A. Imm. B. 6 mm. 
This isa common shell throughout the British Isles. 
It is abundant on pond vegetation and is often found 
eroded by infusoria or covered with a black coating of 
mud. For its association with A. hypuorum and L. glabra 
see the former species. 
Var, ecarindia ( Jef.).. No keel. 
Var. II. d/bida (Nelson). Shell white. 
Monst. scalériforme (Nelson and Taylor). Whorls 
coiled in the form of a screw. 
a. PavoRntex (whirlpool) Linge “Pl. Vis, tf. 7. 
Very flat, glossy, yellowish horn-colour ; zo7r/s 6 to 8; sharply 
keeled. A. 15mm. 5B. 74 mm. 
Found in similar habitats to the last species, but is 
more local. It is very widely diffused throughout the 
British Isles, but is only recorded for Forfar and Caith- 
ness in Scotland. I have noticed that it is much more 
often found with a perfect epidermis than P. sfirorbis, 
even in the same pond as that species. 
It may be distinguished from P. spirorbis by its promi- 
nent keel; it is also flatter and thinner. 
Var. compréssa (Mich.). Thinner and much flatter, 
and more sharply keeled. 
