BY G. I. PLAYFAIR. 127 



This rare form of Coscinodiscus lacustris may possibly con- 

 stitute the genus Perithyra Ehr. 



Var. TYMPANiFORMis, n.var. (PL v., f.30) 



Cellulse a latere cingulato latissimse, saepe rectangulares; lateri- 

 bus planis vel modice convexis, in medio interdum levissime 

 inflatis, nee undulatis. Valvse margine distincta, granulis mar- 

 ginalibus nullis. 



Diam. observ. 40-54; crass. 25-26; lat. zonae 12/x. 



Very broad in girdle-view, rectangular, the angles sometimes 

 sharp, sometimes just rounded ofip; the sides flat, not undulated, 

 but occasionally a little inflated towards the centre. 



Var. Iris (Heribaud & Brun). (PI. v., f.31). 



Diam. 50-70; crass, centr. 16, c. infl. unic. 22, c. infl. binis. 28 /x. 



This answers exactly to Cyclotella Iris Heribaud ife Brun, Diat. 

 Auvergne, Pl.vi., f.l, 3, when allowance is made for the latter 

 being fossil. The outer zone of the valve is striate, with coalesced 

 puncta, one line to each marginal granule, and one intermediate; 

 in the central area, the puncta of the striae are distinct. The 

 total breadth (crass.) across both inflations in girdle-view is just 

 about the same as that in var. tympa^iiformis. In quantity, 

 aUve(9). 



Lismore, type(l, 2, 7, 11, 12, 13, 21); \ar. petlucidus{7, 11); 

 var. stellatus {\l) ; yslv. dentieulatus (7, 12); var. papillatus (6) ; 

 var. tympaniformis (12); var. Iris (7, 9, 12). 



MYXOPHYCE^. 



denus Anab^na Bory. 



ANABiENA OSCILLARIOIDES Bory. 



Cell, carent.; heterocyst. oblong., long. 6, lat. 5; sporis oblongis 

 vel cylindraceis, apicibus rotundatis, immaturis long. 9 12, lat. 6; 

 maturis long. 15-23, lat, 7-8 /x. 



Lismore, swamp (10); not noted in river. 



Forma torulosa, n.f. 

 Fila torulosa diam. 4 /x, cell, truncato-globosis; heterocyst. 

 sphaericis vel ovalibus, diam. 6 /x. 



Lismore (26). Cum var. cylindraced. 



