422 MR JOHN RATTRAY ON A 



Length, 0*0325 mm. ; greatest breadth, 0*0125 mm. ; distance of central 

 nodule from convex side, 0'0075 mm. 



Fam. 2. Navicule^:. 



3. Navicula mesolepta, Kivtz. 



The specimens observed agree almost in every detail with Schmidt's figure 

 (op. tit., pi. xlv. fig. 70), but not with the form which he figures as Navicula 

 (Pinnularia) biceps, Greg., with which he supposes the former to have the 

 closest affinities, if it be not indeed identical. The figures of the forms given 

 by KtiTZiNG (Die Meselschaligen Bacillarien oder Diatomeen, pi. xxviii. fig. 73, 

 and pi. xxx. fig. 34) differ in the more undulated character of the margins and 

 the more distinct appearance of the median raphe. 



Length, 0*0625 mm. ; greatest breadth, 0*0100 mm.; diameter of terminal 

 knobs, 0*0075 mm. ; striae very faint, 14tol5in0 01 mm. 



4. Navicula obtusa, W. Sm., var. lata, nov. (PI. XXIX. figs, la, lb). 



Valve elliptical ; extremities slightly protruded, very obtuse ; marginal 

 flexure between terminal and median areas slight. Striation very faint, 

 running for the most part in a parallel transverse direction, but towards the 

 apices becoming very slightly oblique. Marginal zone of striae leave a sub- 

 elliptical central hyaline area, near the outer boundary of which a band of still 

 more delicate striae occur in the shape of an arch of large curvature. Hyaline 

 areas around the raphe well marked, especially as the centre is approached, 

 but becoming much more constricted towards the extremities, so that the striae 

 almost abut against the raphe. Terminal hyaline spaces subrotund, distinct. 

 Median raphe not very well defined, with very minute central and terminal 

 nodules. Connecting zone (PI. XXIX. fig. lb) broad, with parallel edges, 

 median depression of central area of valve well seen from the zonal aspect. 



Length, 0*0425 mm.; greatest breadth, 0*0187 mm.; length of protruded 

 ends, 0*0050 mm. ; distance between the two central extremities of the median 

 raphe, 0*0050 mm.; diameter of terminal hyaline areola, 0*0043 mm. Striae 

 12 in 0*01 mm. around the margin ; 15 to 16 mm. in the arched bands on the 

 central hyaline space. 



Not uncommon. 



