622 SOME SYDNEY DESMIDS, 



to another plankton-form, viz., St. Manfeldtii var. annulatum, 

 West & West, Frw. Alg. N. Irel. T.'l, f.30, 31, with which it also 

 agrees in size, but differs in the verrucose margins in end-view 



St. armatum, n.sp. (Plate xiii., fig. 10). 



St. mediocre, sinubrevi acutangulato constrictum. Semicelluhe 

 basi inflata angustissima, apice piano, parte superiore corporis 

 utrinque iu radium horizontaliter producta, radiis annulis 5-6 

 granulorum ornatis, apicibus 4-fidis, infra marginem apicalem 

 granulis (ut videtur) geminatis 2 et utrinque granulis solis 2, in 

 serie horizontaliter arcuatim ordinatis, basi inflata annulo granu- 

 lorum instructa. A vertice semicellulse fusiformes, in medio non 

 inflatse, vix isthmo latiores, utrinque aculeis parvis 6 (granulis a 

 fronte visis) munitis. 



Long. 30-36; lat. 48-60; crass, s.ac. 12; lat. isth. 9/x. 



Botany (2, 17), Sydney Water-supply (22). 



St. armatum is nearest in front-view to St. pseudosebaldi* tonsum 

 Nord., for which it may easily be mistaken. It is, however, 

 smaller (mature at 36 x 60 x 12) leaving off, in size, where tonsum 

 begins, the apex is slightly arched, not flat, and there are granules 

 in rings on the rays. In end-view also tonsum is inflated and 

 smooth at the sides. Cf. also St. angolense West & West, Welw. 

 Afr. Alg. T.368, f. 22; St. br achioprominens Borg., Braz. Cent. T 5, 

 f.52; and St. bicorne Hauptfl., in Borges. Bornholm, f.9. 



St. patens Turn., var. planktonicum G. S. West, in Hard}% Frw. 

 Alg. of Vict,, Vict. Nat. xxii., p. 73 



Forma australica mini, (= St. patens Turn., forma austra- 

 lica Playf , in Proc. Linn. Soc. N. S.Wales, 1907, p.189). 



Verba " area centrali granulis geminatis in seriebus 3 concen- 

 trice ordinatis" ut loc. cit. reportavi, potius "area centrali 

 granulis 6 concentrice ordinatis " legenda sunt. 



Forma australica agrees entirely with var. planktonicum except 

 that it has two series of faint apical granules. 



