432 



MR JOHN RATTRAY ON A 



pronounced. (2) The median inflation does not pass directly into the proximal 

 region of the frustule, but is definitely limited by a second proximal constriction, 

 Avhich is well marked. (3) There is a distinct proximal inflation. (4) Whilst 

 the striation is arcuate and radiating in the distal area, it is radiating, but 

 straight, in the median, and similar, though much less pronounced, in the 

 proximal. The striation of the median region does not, therefore, pass un- 

 interruptedly into that of the proximal, but is almost as clearly separated from 

 it by an area at the proximal constriction, in which the striation is perpendi- 

 cular to the longitudinal axis, as the striation of the median inflation is from 

 that of the distal by a similar arrangement. The median nodule is prominent, 

 but the raphe is only faintly marked throughout the remainder of its course. 



Length of distal inflation, 

 „ median „ 

 f, proximal „ 

 „ apical crest, 

 Breadth of distal inflation, 

 „ „ constriction, 



„ median inflation, 



„ proximal constriction, 



„ „ inflation, 



Strisein 0*01 mm. = 10. 



0-0100 mm.^i 



0-0137 „ 



0-0150 





0-0025 



» 



o-oioo 



, 



0-0043 



, 



0-0075 



, 



0-0030 



> 



0-0043 



> 



entire frustule = 0-0412. 



Rare. 



Fam. 4. Cocconeide^e. 



23. Achnanthidium fiexellum (Klitz., de Breb.). 

 = Cocconeis thwaitesii, W. Sm. 



Not uncommon. All the specimens essentially agree with the type figured 

 by W. Smith (op. tit, vol. i. pi. iii. fig. 33), the only circumstance of importance, 

 by which some forms in the deposits may be distinguished, being the absence 

 of the somewhat prominent circles of marginal puncta, or the very indistinct 

 character of these. 



Average length, 00425 mm.; breadth, 0*0175 mm.; breadth of terminal 

 obtuse extremities, 0*0075 to 0-0085 mm. 



24. Cocconeis placentula, Ehrenb. 



Not uncommon. Valval ornamentation very faint, but raphe and central 

 nodule well marked. Length, 0*0275 mm. ; greatest breadth, 0-0175 mm. 



