SYSTEMATIC ACCOUNT 235 



Melosira sulcata (Ehrenberg) Kutzing. 



Kiitzing, 1844, p. 55, pi. 2, fig. 7. 



Hustedt, 1928, p. 276, fig. 119. 



Gallionella sulcata Ehrenberg, 1838, p. 170, pi. 21, fig. 5. 



Orthosira marina Wm Smith, 1856, p. 59, pi. 53, fig. 338. 



Par alia marina Heiberg, 1863, p. 33. 



Orthosira sulcata O'Meara, 1875-77, p. 252. 



Cells discoid, often united together in long chains. Valves shaped like a plate, the 

 central area slightly convex, valve mantles curved, bearing coarse granular markings, 

 central area of valve face bearing short radial lines, which in some cases are reduced 

 to a ring of irregular pearls. Chromatophores : numerous small plates. Diameter of 

 valve 60-68/x ; pervalvar axis 7-8/x. 



Neritic and littoral, tychopelagic. Wide distribution in Arctic and European waters, 

 was observed but rarely in Antarctic material. 



Observed at St. 681. 



Genus Hyalodiscus Ehrenberg 

 Ehrenberg, 1845 



Hyalodiscus chromatoaster Karsten. 

 Karsten, 1905, p. 74, pi. 2, figs. 4, 5. 



Cells discoid, valves convex, sometimes deeply so. Central area of valve dif- 

 ferentiated, furnished with fine granules irregularly arranged or scattered. Diameter 

 of central area approximately half the total diameter of the valve. Peripheral zone finely 

 striate, striae moniliform, oblique. Peripheral zone surrounded by finely striate margin, 

 striae radial. Girdle composed of numerous annular segments. Chromatophores: 

 numerous large stellate or lobed bodies. Diameter of valve 80-1 10/x, mostly 95-100/x ; 

 pervalvar axis 48^. 



A bottom form frequently found in the plankton, neritic. A characteristic Antarctic 

 diatom. 



Observed at St. 482. 



Hyalodiscus kerguelensis Karsten. 

 Karsten, 1905, p. 74, pi. 2, figs. 6, 7. 

 Cells discoid, valves somewhat deeply convex, central area of valve differentiated, 

 furnished with fine and somewhat indistinct granules arranged irregularly or in radial 

 lines. Diameter of the central area varies greatly, but is usually about half the total 

 diameter of the valve. Peripheral zone finely striate, striae moniliform, radiate, granules 

 in quincunx. Peripheral zone surrounded by a strong marginal flange, strongly striate. 

 Girdle composed of numerous annular segments. Chromatophores : numerous spatu- 

 late or lobate bodies. Diameter of valve 95-145^, mostly 140/x ; pervalvar axis, usually 



IIO/^. 



Although frequently found in the plankton this species must be regarded as a bottom 



