424 MR JOHN RATTRAY ON A 



attenuated to very sharp acicular points. (3) The central nodule on one side 

 of, and between, the proximal extremities of the raphe is not round in outline, 

 but slightly reniform or flattened towards the margins of the frustule, but 

 rounded at its ends. (4) The transverse diameter of the costae is somewhat less. 

 Length, 0*2625 mm.; greatest breadth, 0*0450 mm.; diameter of terminal 

 areolae, 0*0075 mm.; diameter of transversely directed costae, 0*0020 to 

 0025 mm. 



9. Navicula major (W. Sm.). 

 = Pinnularia major, W. Sm. 



Common. The following are the peculiarities of some of the specimens 

 from the deposit : — (1) The central hyaline area does not form a more or less 

 elliptical space around the central nodule, there being merely a slight expan- 

 sion, which is sometimes confined to one side only (Schmidt, op. cit., pi. xlii. 

 fig. 17). (2) The terminal hyaline areola is not subrotund, but is, at both 

 extremities of some of the specimens, of sharply reniform outline, arising from 

 the elongation into it of one of the subterminal costae. One side of the areola 

 is larger than the other. (3) On the proximal side of the terminal areolae the 

 costae extend almost up to the median raphe. (4) The costal halo is arched 

 over the central nodule, but less markedly so than figured by Van Heurck 

 (op. cit., pi. v. fig. 3). (5) The direction of the subterminal costae is more oblique 

 than is figured either by Van Heurck or W. Smith. 



Length, 0*1225 mm. ; greatest breadth, 0*0180 mm. ; distance between 

 central ends of raphe, 0*0025 mm.; transverse diameter of terminal reniform 

 nodules, 0*0050 mm. 



10. Navicula viridis (Ktitz., W. Sm.). 



= Pinnularia viridis, W. Sm. 



Common, and of various sizes. The peculiarities of some of the specimens 

 are : — (1) The well-defined subrotund hyaline terminal areolae. (2) The disposi- 

 tion of the costae, which run obliquely outwards and towards the central trans- 

 verse axis at the extremities, but obliquely outwards and away from that axis 

 towards the centre. (3) Two or three of the costae on the proximal side of the 

 terminal areolae extend close up to the median raphe. (4) The central nodule 

 is but faintly defined, sometimes the inner ends of the costae in the region bound- 

 ing the clear central space form an almost straight line, whilst their shorter 

 length on the opposite side is often not very marked. (5) The general outline 

 of some of the specimens is much less rounded than that of those figured by 

 A. Schmidt (op. cit, -pl.xlii. figs. 19-21). They present, however, certain affinities 

 to Navicula alternans, Schum., both with respect to ornamentation and to the 



