44 BRITISH FRESHWATER RHIZOPODA. 



MURRAY in Proc. Roy. Soc. Edinb., XXY (1905), pp. 609, 615 ; in 



Ann. Scott. Nat. Hist. 1907, p. 96 ; in Bathym. Surv. Scott. Lochs, 



I (1913), p. 326. 



ODELL in Ottawa Natur. XIX (1905), p. 19. 

 EVANS in Proc. E. Phys. Soc. Edinb. XVII (1907), table 1. 

 BROWN in Jrn. Linn. Soc., Zool. XXX (1910), pp. 362, 366 ; in Ann. 



Scott. Nat. Hist. 1911, pp. 229, 231 ; in Naturalist, 1912, p. 182; in 



Scott. Natur. 1913, p. 208. 

 HEINIS in Arch. Hydrobiol. V (1910), p. 109. 

 HOPKINSON in Irish Natur. 1910, p. 3. 



WAILES & PENARD in Proc. B. Irish Acad. XXXI, LXV (1911), p. 18. 

 WAILES in Scott. Natur. 1912, p. 61; in Jrn. Linn. Soc., Zool. XXXII 



(1912), pp. 126, 150 ; in Naturalist, 1913, p. 148. 



Test large, ovoid, hyaline, compressed ; transverse 

 section lenticular ; formed of oval or sub-circniar 

 silicious scales regularly imbricated and arranged in 



FIG. 128. Body-scales of Placocista spinosa. x 1000. 



alternating longitudinal rows ; aperture linear with un- 

 dulate margins formed by sub-circular scales; margin 

 of test furnished at regular intervals with lanceolate 

 spines, either solitary or in pairs, attached to the test 

 at the imbrications of the scales by small hemisphe- 

 rical nodules ; nucleus large, placed posteriorly ancU 

 containing a single nucleole ; two contractile vesicles 

 generally visible; plasma colourless, granular, some- 

 times containing Zoochlorellde in symbiotic relationship, 

 partly filling the test; pseudopodia numerous, filose, 

 branching. 



Length 116-174 //,; breadth 71-100 /x ; aperture 

 35-70 JJL ; thickness two thirds to one half the width ; 

 body-scales 12-20 /A in length, 7-10 ^ in breadth; 

 spines 5-35 /u, in length ; nucleus 22-35 /x in diameter. 



Habitat. -Sphagnum. 



ENGLAND. Cumberland (Broiun) ; Westmorland 

 (West, Brown) ; Lancashire (West) ; N. and W. York- 

 shire ; Shropshire ; Isle of Wight ; Cornwall. 



