16 81. FLUVIALES. 



Native. Lacustral. I have not myself seen this spe- 

 cies at any considerable elevation ; but it is reported to 

 occur in MaUiam Tarn, in Yorkshire, which is upwards 

 of 400 yards above the sea. Seems likely enough to oc- 

 cm* in South Wales, being known in several of the neigh- 

 bom-ing counties, as Somerset, Gloucester, Hereford, 

 Saloj), Cheshire, and Anglesea. 



1126. POTAMOGETOX LUCENS, LinU. 



Area 1 3 3 4 5 * 7 8 9 10 11 12 13 14 15 * * [18]. 



South limit in Devon, Isle of Wight, Kent. 



N. limit in Banff, Perth, Lanark. [Shetland? Orkney ?] 



Estimate of provinces, 15. Estimate of counties 60. 



Latitude 50 — 58. British type of distribution. 



Agrarian region. Inferagrarian — Superagrarian zones. 



Descends to the coast level, in the Peninsula. 



Ascends to 100 or 200 yards, in England. 



Range of mean annual temperature 51 — 46. 



Native. Lacustral. Said to occur so far northward as 

 Shetland (Edmondston) and Orknej'^ (Lowe's list) ; but ve- 

 rification would be desii-able before implicitly relying upon 

 these habitats, reported only upon unsafe authority. The 

 Whey Sike, in Teesdale, where this si^ecies has been 

 reported to occur- (Flo. N. D.) may be above 200 yards of 

 altitude ; but I am unaware what is the true elevation of 

 that alleged locality. 



1127. POTAMOGETON PR^LONGUS, Wulf. 



Area * * 3 4 5 * * 8 * 10 * 12 * 14 15. 

 South limit in Berkshire, Essex. 



