QUADRULEf.LA SYMMETRIC A. 63 



Hal'itat. Sphagnum. 



KXGLAXD. Goathland, N. Yorkshire. 

 SCOTLAXD Loch Ness (Peiiard). 

 IRELAND. Inishbofin, Gal way. 



The typical Q. si/mmftrica varies considerably in 

 form, the outline in broad view ranging from a some- 

 what wide pyriform shape with convex sides to an 

 elongated form with slightly concave sides ; the var. 

 irregulars resembles the latter in shape, but the sides 

 are nearly or quite straight and the size is considerably 

 larger. 



It is not common, and records of its occurrence are 

 so far restricted to the British Isles and the United 

 States of America, where Periard first found it in the 

 Rocky Mountains (10,000 ft.) and where it also occurs 

 in the Eastern States. 



It has been suggested that the genus Quadrula 

 (Qnai.lrnlella) rightly belongs to the genus Ni'bela, 

 and this opinion has recently received further support 

 by the discovery in North and South America and in 

 the Tropics of intermediate forms which have been 

 recorded under the names of Nebela tropica Wailes 

 and Nebela sciitellata Wailes. 



1. Heleopera sordida Penard. 

 (Plate LXIL figs. 10 and 11.) 



Heleopera sordida 



PENARD in Rev. Suisse Zool. XVIII, 4 (1910), pp. 931-932, pi. viii, 



ff. 2, 3 ; in Brit. Antarct. Exped. I, Biol., 6 (1911), p. 236. 

 WAILES & PENARD in Proc. R. Irish Acad. XXXI, LXV (1911), p. 17. 

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



XXXII (1912), pp. 125, 143, 156; toe. cz7.(1913),p.213; in Naturalist, 



1913, p. 146. 



Test small, of a yellow colour, chitinous, ovoid, 

 compressed, smooth except for a few adherent particles 

 on the fundus which consist of silicious and vegetable 

 matter ; aperture wide, in side view notched or with 

 the lips closed together ; plasma clear and colourless, 

 the anterior portion granular ; nucleus large, granular, 



