TUBULAR I A. 



GENUS 57 fe.-TUBULARIA BRUN, 1894. 



By the side of Dimargramma should be placed, 

 according to Prof. Brun, a new genus, which he 

 has described under the name of Tubularia Brim, 

 in Le Diat., 1S94, ii., p. 88. 



Frustule tubular, somewhat twisted, flat on 

 the girdle face. Valve transversely striated : raphe 

 obscure ; apices opening obliquely and furnished 

 with a large hyaline space. 



Only one species up to the present time. 



Tubularia pistillaris J. Brun, found in 

 Jackson's Paddock (Barbo). Very rare. Repre- 

 sented in the text. 



Fig- 94- 



Tubularia pistillares. 



GENUS 58. PLAGIOGRAMMA GREV, 1859. 



Valve having at the median portion a hyaline 

 space, which is generally transverse, often furnished 

 in the middle with a pseudo-ocellus or furnished with 

 two robust costse, which are prominent in the girdle 

 face : apices hyaline ; striae punctate, puncta distant. 

 Frustules united in filaments. 



The Plagiogramma are amongst the most beautiful 

 examples of diatoms. About 50 species are known and these inhabit southern 

 regions. The two about to be described are the only species peculiar to the 

 North Sea. Among the Plagiogramma are also included two species of 

 Denliciila, D. intetrupta, and D. icvis of Gregory, found in Lamlash Bay, 

 Scotland, but they are very problematical species, the valves of which have 

 not been described. 



Fig- 95- 

 Plagiogramma 

 Gregorianum. 



ANALYSIS OF SPECIES. 

 Striae formed of coarse puncta sub-quadrangular; pseudo-ocellus broad, 



girdle face scarcely or not attenuate at the apices 



. P. Gregorianum. 



I Stria? formed of small puncta ; pseudo-ocellus narrow, girdle face strongly 

 i_ attenuate at the apices .... 



P. Van Heurckii. 

 Y 



