204 ' MR. G. H. WAILES ON FRESHWATER 



large, about four or five in number ; two or more contractile vesicles usually 

 present ; pseudopodia not observed. 



Diameter 120-135 /i ; aperture 48-55 jjl ; thickness about one quarter oi 

 the diameter. 



• Distribution. — Norfolk, Virginia ; Jacksonville, Florida {Leidij) ; Switzer- 

 land (Penard). 



In the material from Norfolk the curved tests at once attracted attention, 

 and that this is not merely an accidental condition is evidenced by the 

 constant curvature and the absence of any similar tests not curved. The 

 number of the nuclei also distinguishes it from other Arcellce, a subject 

 which is entered upon at greater length in the note on the following species. 



No active and only a few living individuals were observed, and further 

 observations as to the number of nuclei and the plasma, etc., are desirable. 

 Penard has observed this species in two localities near Geneva ; at Norfolk 

 it occurs numerously but is perhaps of very local occurrence. 



Arcella megastoma, Penard, sp. nov. (PL 15. figs. 1 & 2.) 



A. polypora pars, Penard (8), p. 408. 

 A. polypora pars, Wailes (16), p. 130. 

 A. discoides, Elireub. pars, Leidy (6), p. 173, pi. 28. fig. 22. 



Test large, circular, compressed, thickness about one quarter to one third 

 of the diameter ; aperture large, circular, invaginated, surrounded by 

 numerous small pores, from 0*4 to more than 0*5 of the diameter of the test 

 in width ; plasma greyish in colour, granular, attached to the test by numerous 

 ■epodes and containing many food-particles ; nuclei small, numerous, from 40 

 to 200 in number ; several contractile vesicles usually present ; pseudopodia 

 digitate. 



Diameter 190-365 /x; aperture 100-190 /a. 



Distribution. — Van Gortlandt Park, N.Y.; Split Rock, Lake Boonton, N.J.; 

 'W jormxig (Leidif); Chili; Switzerland (PgnanZ). 



Having received slides containing specimens found near Geneva, kindly 

 sent to me, for comparison with American specimens, by Dr. Penard, he 

 suggested that I should give a description of this species, which he had 

 named provisionally A. megastoma ; it is, however, to be hoped that he will sup- 

 plement it by the results of observations extending over a considerable period. 



All species of Arcellas have normally two nuclei only, except A. lyolyjjora, 

 A. megastoma, and ^1. curvata ; the first two belong to what may be called 

 the A. discoides group, having tests more or less similar to that species but 

 possessing more than two nuclei : ^1. discoides, howeYer,has been recorded by 

 several observers with more than two nuclei (8. p. 408;, for example Leidy (6), 

 PI. 28. fig. 28, shows a test 180 /m in diameter with three nuclei, but others may 

 have escaped observation, and in other respects it conforms to A. 2^olypora ; 



