PLAOOOISTA SPINOSA. 



45 



Wales. — Snowdon (West), Llyn Crafnant and 

 Dolgam, Capel Curig {Hoph. coll.), Carnarvonshire; 

 Towyn, Merionethshire (Gash). 



Scotland. — Shetlands ; ■ Hebrides ; Inverness-shire 

 and Aberdeenshire (Brown) ; Perthshire (Gash, Broivn) ; 

 Argyllshire (Broiun) ; Midlothian (Gash) ; Wigtown- 

 shire (Brown). 



Ireland. — Clare Island and mainland, Mayo; G-al- 

 way; Wicklow (Archer, Hoph.); Kerry (Archer). 



In the British Isles this species is found at all alti- 

 tudes at vfhich sphagnum flourishes and is perhaps 

 more numerous at the higher elevations (i. e. 800- 

 2000 ft.). Freshly gathered sphagnum is the best 

 material in which to seek active individuals. The 

 pseudopodia are seldom seen. 



The ZoochlorellsB occasionally found in the plasma 

 have the appearance of being perfectly healthy and of 

 living there symbiotically. 



Fia. 129. — Various types of spines of Placocista spinosa. o-c, x 800 ; 

 dr-f, X 1040 (after Penard) ; f, side view. 



The small, button-like processes (fig. 129 a-c) by 

 which the spines are attached to the test are of a 

 chitinous nature and are dissolved by strong sul- 

 phuric acid whilst the silicious scales and spines 

 remain unaffected. The spines are usually solitary 

 but may arise in pairs or rarely in threes ; they are, 

 except very rarely, flattened, and vary in broad view 

 from linear to lanceolate in shape ; the broad view is 

 always approximately in the plane of the broad view 



