20 BEITISH FRESHWATER HELIOZOA. 



usually single ; pseudopodia radial, numerous, straight, 

 each containing a stiff axis originating from near the 

 nucleus. 



Since microscopes of any considerable power first 

 came into use references to this genus are very 

 numerous. 



Heliozoa were at first known as " Sun animalcules," 

 and this popular term is still in use. The name 

 Trichoda sol 0. F. Miiller (1773) was probably applied 

 indiscriminately to various spherical forms with 

 radiating pseudopodia ; one of these, and perhaps the 

 one most frequently met with, was distinguished by 

 Ehrenberg (1830) under the name of Actiiioph.rys sol. 

 This species, which is decidedly variable in appearance, 

 has since then received a bewildering number of names,, 

 and forms have b^en identified with it which may 

 belong to other species of Actino'phrys or even to species 

 in other genera, but in the absence of sufl&cient details 

 of specific value in the descriptions given by their 

 authors we can only assume that they refer to the 

 Heliozoan most commonly found. 



Three species are comprised in this genus : 



A. vesicidata Pen. is similar to A. sol, but usually smaller, 

 being about 30 i^. in diameter; the contractile vesicles emerge 

 from the periphery and become pendulous before collapsing. 



A. paradoxa Carter is probably a species of Cochliopodium. 



Synopsis op British Species. 



Plasma containing numerous large vacuoles ; diameter 40 /j. 

 to 50 f.. (1) J. sol. 



Plasma without vacuoles ; diameter 40 /a to 60 fi. 



(2) A. fiuhalpina.. 



1. Actinophrys sol Ehrenb. 



(Plates LXIV, figs. 1-3, LXVII, figs. ]-(i, 

 LXXII, figs. 1.) 



'<t Trichoda huI (part) 



MuLLEK Verm. terr. fluv. I, 1773, p. 76. 



