322 



THALASSIOTHRIX. 



\ 



Fig. 78. 



Thalassioth rix longisiima 

 var. antarctica. 



This genus is confined to marine species. Mr. 

 Grunow in the first instance also included in it 

 Synedra Nitzschioides. But now the genus should 

 only consist of Th. Frauenfeldii Grun. (H.V.H. 

 Atl., pi. 37, f. 11 and 12*), plate 30, fig. 839, 

 and Th. longissima CI. and Grun. (fig. 78), 

 the longest known diatom since it attains to 3 to 4 

 mm. in length. It inhabits the Arctic Seas. 



Thai, curvata Castr. (Diat. Challenger, p. 55 

 pi. 24, f. 6*), plate 30, fig. 840, is too incom- 

 pletely described and figured to form a judgment, 

 on the form, without at least having an authentic 

 specimen at one's disposal. According to the 

 figure it does not appear to differ much from 

 Synedra (Thalassionetna) Nitzschioides, if it were not 

 for the slight flexure of the frustules. 



Tribe VIII. Fragilakie^e. 



\ 



Frustules rectangular in girdle view ; valves with distinct pseudo-raphe, 

 regularly striated ...... Fragilaria. 



Girdle face f Frustule with connecting zone undulate-arcuate, valves 



rectangular. lanceolate ..... CymatOSira. 



Valves with -j 



! scattered | Frustules with valves arcuate, connecting zone arcuate and 



I puncta. ( attenuated near the apices, which are inflated . Campyloaira. 



