344 DISCOVERY REPORTS 



Navicula astrolabensis Hendey, sp.nov. (PI. IX, figs. 14, 15.) 



Valvis lineari-lanceolatis vel anguste ellipticis; apicibus rotundatis, notulis duobus 

 lobatis instructis; raphe recta, angusta; striis transversis, obliquis, decussatis (Pleuro- 

 sigmatis ad instar), subtilissimis, raphen non attingentibus ; nodulo centrali parvo, area 

 circulari cincto ; nodulis terminalibus parvis. Mensura valvarnm 280 x 30/i . 



Hob. in aquis marinis " Bransfield Strait", prope insulam "Astrolabe" dictam, in 

 oceano Antarctica. 



Typus in Herb. Mus. Brit. No. 33963. 



This species occurred in small quantities in the material obtained at St. WS 481 

 where the net touched bottom. It is not a true member of the plankton, but a bottom 

 form. In this it is near Pleurosigma, to which it bears a striking resemblance, particularly 

 in the arrangement of the moniliform striae upon the valve surface. Some workers have 

 included such species in the genus Pleurosigma despite the fact that the valves do not 

 show the characteristic sigmoid flexure. 



Observed at St. WS481. 



Navicula corymbosa (Agardh) Cleve. 



Cleve, 1895, p. 26. 



Schizonema corymbosum Agardh, 1824, p. 11. 



Cells small, usually united in fine branched mucous tubes. Valves lanceolate in out- 

 line, apices very slightly produced, obtuse. Axial and central areas indistinct. Striae 

 very fine, slightly radiate. Connective zone simple, narrow. Chromatophores : several 

 rounded bodies. Apical axis of cell 10-12/M. 



Observed near St. 560. 



Navicula lyra Ehrenberg. 



Ehrenberg, 1843, p. 419, pi. 1, fig. 9 a. 

 Kiitzing, 1844, p. 94, pi. 28, fig. 55. 

 Cleve, 1895, p. 63. 

 Mann, 1907, p. 347. 



Cells usually large. Valves elliptical with rounded or slightly rostrate apices. Raphe 

 distinct, surrounded by a narrow hyaline axial area which dilates to form a short 

 stauros around the central nodule. The hyaline stauros is continued to produce lyre- 

 shaped sulci which proceed towards the rounded apices of the valve. The valve surface 

 is furnished with fine puncta, with the exception of the sulci. In the narrow areas be- 

 tween the raphe and the sulci the puncta are in straight parallel rows, in the areas be- 

 tween the sulci and the valve margin they are very slightly radiate. Connective zone 

 simple. Apical axis of cell 120-140/u, ; transapical axis 6oju. 



Mann (1907) said "It is plain that this polymorphic form has no hard and fixed 

 boundaries, and that what is to be included, or what not, must always be somewhat a 

 matter of personal preference." One of the most ornate species of the genus Navicula, 

 it is found in both fossil and recent material, and has a world-wide distribution. Cleve 

 (1895) gives nineteen varieties and forms of this species, and said of the Lyratae "All 



