ACANTHOCYSTIS. 51 



pellucid oval spicules arranged tangentially and of the bases 

 of long radial spines which are cylindrical and truncate ; 

 plasma bluish in colour. Diameter of body 13 ju to 16^; 

 radial spines 20 /JL to 30^ in length. 



A. pectinata Penard. Body small; envelope normal; the 

 radial spines short, tenuous and all of equal length; plasma 

 bluish in colour ; pseudopodia very long, tenuous. Diameter 

 of envelope 15 /m to 18 ^ ; spines about 3 /m in length. 



A. ludibunda Penard. Envelope formed of a single layer 

 of silicious spherules ; the radial spines acicular with enlarged 

 bases similar to pin-heads ; plasma filled with red coloured 

 granules. Diameter of envelope 28 /./ to 35 /m ; length of 

 spines 7 fj. to 10 fj. ; diameter of spherules about 2 /u. 



SYNOPSIS OP BRITISH FRESHWATER SPECIES. 



(a) Spines of two kinds, long and short. 



Spines forked. (1) A. chtetophnra. 



(b) Spines all of one kind. 



Spines short and curved. (2) A. erinaceus. 



straight and slender. (3) A. spinifera. 



straight or slightly curved, short. 



(4) A. brevicirrhis. 

 long, tapering-, very numerous. 



(5) A. myriospina. 



1. Acanthocystis chaetophora (Schrank). 

 (Plate LXXI, fig. 1 ; PI. LXXII, fig. 2.) 



Trichoda clixtoplioru 



SCHRANK, Fauna Boica, Ingolstadt, 1803, p. 93. 

 Actinoph rtjs viridis 



EHRENBERG Abh. Akad. Berlin, 1833, p. 228. 

 Acanllwcystis turfacea 



CARTER Ann. Mag. Nat, Hist. (ser. 3) XII, 1863, p 263 ; op. cit. XIII, 

 1864, p. 36, pi. ii, f. 25. 



WAILES Jrn. Linn. Soc, Zool. XXXII, 1912, p. 126. 



PENARD Heliozoaires, 1904, p. 235, figs. 

 A. viridis 



GRENACHER Zeitschr. wiss. Zool. XIX, 1869, p. 289, pi. xxiv, ff. 1-3. 

 A. pallida 



GREEFF Arch. mikr. Anat. V, 1869. p. 489, pi. xxvii, f. 19. 

 A. chastophora 



LEIDY Rep. U.S. Geol. Surv. XII, 1879, p. 264, pi. xliii, ff. 1-6. 



WEST Jrn. Linn. Soc. Zool. XXVIII, 1901, p. 340. 



Body spherical, with a double outer investment, the 



