584 Annals of the South African Museum. 



fiexuosis ; pseudpramis elongatis, patescentibus, saepe primo adpressis ; 

 vaginis crassis, plus minus lamellosis, parte exteriore difttuente hyalina, 

 parte iuteriore firma fusca vel nigro-fusca, apicem versus attenuatis, 

 semper apertis ; trichomatibus saepe 2-)! parumper intra eandem 

 vaginain (iis deinde divergentibus vel evanescentibus), nonnunquam 

 rertis nonnunquam spiraliter contortis, contentu granuloso, ad dissepi- 

 nienta constrictis, apicem versus paullo attenuatis, non in piluin 

 productis, cellulis tarn longis quam latis vel brevioribus ; heterocystis 

 singulis, basilaribus, conicis vel subhemisphaericis. 



Crass, fil. ram. apical., 12-16 /x; eras.-, trich., 5-7 fi; lat. heterocyst., 

 6-7 /x ; crass, vag., usque 6 \x. 



Sample 44. 



This is a larger species than D. fusca and is characterised by more 

 markedly divergent and flexuous branches (Fig. 39, ^4). As a result, 

 the plant presents a more irregular appearance, and fails to exhibit the 

 pronounced penicillate habit of the previous species. There are two 

 other distinctive features, viz. the nature of the sheath and the 

 remarkable spiral coiling of the trichomes (Fig. 39, D). The sheaths 

 consist of a diffluent outer portion which is colourless, and of a much 

 firmer inner portion which is deep brown to blackish-brown (Fig. 39, 

 C). The sheaths are in general thick, the trichomes being very 

 narrow, as compared with the width of the filaments (Fig. 39, C, D). 

 The spiral inrolling of the trichomes is a local phenomenon, but is 

 sufficiently frequent not to escape one even in a cursory examination. 

 The sheaths are often irregularly inflated at the points where this 

 spiral inrolling occurs. It is to be noticed that the inner coloured 

 portion of the sheath is involved in the spiral torsion, only the outer 

 hyaline part being unaffected (Fig. 39, D). 



IV. BACILLARIEAE (DIATOMALES). 



(^) CENTRIC 'AH. 

 (1) MELOS1BACEAE. 



Genus MELOSIKA Agardh. 



1. Melosira varians, Ag. ; Van Heurek, Synops. Diat. Belg., 1880-85, 

 p. 198, PI. LXXXV, figs. 10. 11. 14, 15. 



•Samples 25 (rather common, with auxospores), 33 (rare). 



