64 BRITISH FKESHWATER HJiLIOZOA. 



colour, granular -without a clearly defined endoplasm ; 

 nucleus not large, grey in colour, placed eccentrically ; 

 contractile vesicle large with a ■ smaller one often 

 present ; pseudopodia long, tenuous, granuliferous. 



Diameter of envelope without spines 18 /a to 23 /x ; 

 length of spines one fourth to one half the diameter 

 of envelope. 



Habitat. — Aquatic vegetation. Rare. 



Distribution. — Scotland. — Isle of May {Brown). 



Ireland. — Clare Island, Mayo {Wailea Sf Penard). 



From A. aculeata and A. brevicirrhis this species is 

 distinguished by its smaller size and much more 

 delicate capsule as also by the curved radial spines 

 which are quite distinctive. 



3. Acanthocystis spinifera Greeff. 

 (Text-fig. 190.) 



Acanthocystis spinifera 



Grbbff Arch. mikr. Anat. V, 1869, p. 493, pi. xxvii, fl. 20-23. 



Archer Qi-t. Jrn. Micr. Sci. X, 1870, p. 102 ; op. cit. XVI, 1876, 

 p. 364, pL xxi,f. 8. 



Hbrtwig & LbsseSr Arch. mikr. Anat. X, 1874, Suppl. p. 195, pL iv, 

 f . 3, a, b ; non Pbnard Heliozoaires, 1904, p. 245, fig. 

 ? A. pertyana 



Pbnard Heliozoaires. 1904, p. 248, fig. 

 Acanthocystis 



? Lbidy Rep. U.S. Geol. Surv. XII, 1879, p. 268, pi. xliii, ff. 7-13. 



Body of medium size, spherical, with an outer invest- 

 ment formed by the enlarged bases of numerous, 

 moderately long, straight, tenuous and sharply pointed 

 spines placed radially ; an inner investment also present 

 formed of small elliptical scales ; ectoplasm and endo- 

 plasm clearly differentiated, the former granular and 

 frequently containing one or more yellow bodies or 

 numerous green granules ; the endoplasm containing a 

 central granule and an eccentrically placed nucleus 

 containing a nucleolus ; contractile vesicles, one or 

 more situated near the periphery, but often indistin- 

 guishable ; pseudopodia long and very tenuous. 



