NEBELA BIGIBROSA. 57 



tr 



Three other species of Nebela, viz. N. martiali, 

 N. certesi, and N. inurrayi, are characterized by the 

 two pairs of orifices in depressions in the sides of the 

 tests and the tubes connecting each pair. The two 

 last-mentioned species have been recorded from the 

 Southern Hemisphere only ; N. bigibbom from the 

 Northern Hemisphere only, where it usually occurs in 

 elevated situations. 



2. Nebela griseola Penard. 

 (Plate LXI, figs. 14-16.) 



Nebela griseola 



PENARD in Brit. Antarct. Exped. I, Biol., 6 (1911). pp. 244-245, 



pi. xxiii, f. 8. 

 WAILES & PENARD in Proc. R. Irish Acad. XXXI. LXV (1911), pp. 9, 



18, 47-48, pi. v, f. 25 a-g. 

 WAILES in Jrn. Linn. Soc., Zool. XXXII (1912), pp, 125, 138. 



Test small, pyriform, slightly compressed, com- 

 posed of variously-shaped plates and silicious grains; 

 aperture usually circular and bordered by a prominent 

 collar, semicircular in section ; plasma clear, colour- 

 less, containing starch-grains and food -particles, also 

 occasionally reserve materials ; nucleus small, placed 

 centrally, containing numerous small nucleoles ; one 

 or two contractile vesicles usually present. 



Length 80-87 ju ; breadth 52-60 /x; thickness 45- 

 55 /x; aperture 18-23 /x; collar 27-32 /x in diameter; 

 nucleus 12 /x dia. 



Habitat. Sphagnum and mosses. 



IKK LAND. Achill Island and Clare Island, Mayo. 



The resemblance to N. tenella is somewhat close, 

 but this species is distinguished by the slighter com- 

 pression of its test, larger aperture, and (usually) 

 larger size. The ratio of the transverse axes in 

 JV. tenella is from 4 : 3 to 2 : 1, in N. griseola it is 5 : 4. 

 The only other species of Nebela with a similar collar 

 around the aperture is N. cratera Wailes, in which 

 the test is not compressed and is 120-140 /x in length. 



