122 CHAPTER I 



PHYSA HETEROSTROPHA Say 



t Genp., Czechosl., Holl., Denm. Manit.-Nfld., U.S.A. E of Mississ. 



(mainly hothouses). 



Planorbidae 



GYRAULUS (aRMIGER) CRISTA L. 



Brit. Isl., Eur. E to C Russia, N. Afr., Alas.-Ont., NE U.S.A. 

 WSib. 



GYRAULUS GREDLERI Bielz (incl. borealis Loven, syn. arcticus Beck) 



Eur. (boreoalpine), N & C Asia E to Alas.-Labr.; Greenl. 



Kamch. (Glacial subfossils in the Brit. 



Isl.) 



GYRAULUS (torquis) PARVUS Say^ 

 t Denmark (aquarium). Alas.-E Can., S to Florida, Nfld. 



helisoma duryi Weth. (incl. eudisciis Pilsb.) 

 t Engl, (aquarium). Florida. 



HELISOMA (PIEROSOMA) TENUIS Phil. 



t Denmark (aquarium). Calif., Mexico. 



HELISOMA (pierosoma) trivolve Say 

 f Moscow (aquarium). Alas.-E Can. & Maine, S to Missouri. 



Valvatidae 



valvata piscinalis O. F. Miill. 



Brit. Isl., Eur. (generally), Cauc, f NE U.S.A., E Can., Nov. Scot. 



Hither Asia, W Sib. 



Amnicolidae 



BULIMUS (biTHYNIA) TENTACULATUS L. 



Brit. Isl., Eur. (generally), N. Afr., (f) NE U.S.A., E Can., W to Wise* 



Cauc, W Sib. 



^ Sometimes regarded as a sbsp. of the Palaearctic G. laevis Aid. 



'^ Baker (1928, p. 81) described a new and possibly indigenous sbsp. of Bulimus tenta- 

 ciilatus from N. America but its state seems doubtful (La Rocque, 1953). 



