438 MR JOHN RATTRAY ON A 



Fam. 6. Tabellarie^e. 



41. Tabellaria fenestrates, Kiitz. 



Rare, and sometimes in fragments. Typical. Length, 0*0600 mm. ; breadth 

 of terminal inflation, 00500 mm. ; breadth of median inflation, 0-0055 mm. ; 

 breadth of intermediate area, 00030 mm. 



42. Tabellaria jlocculosa, Ktitz. 



Rare. Typical. Length, 0*0300 mm. ; greatest breadth (a) at central 

 inflation, 0*0050 mm. ; (J3) at terminal inflations, 00035 mm. ; breadth of inter- 

 vening portion, 0*0030 mm. Striation very faint. 



Fam. 7. Surirelle^e. 



43. Surirella nobilis, W. Sm. 



Very common, and of variable dimensions. The outline is ovate, the 

 margins being more or less rounded and sometimes flattened. The arrange- 

 ment of the alee and canaliculi is in many cases essentially the same as in 

 Smith's figures (op. cit., vol. i. pi. viii. fig. 63), but in several frustules variations 

 are found around the wider extremities of the valves. The canaliculi, namely, 

 are not bounded by straight lines, but become very arcuate, and for a space 

 occupied by three of these give the valve a scale-like appearance (PI. XXIX. 

 fig. 10). The median reniform hyaline terminal areola is separated by a small 

 lenticular hyaline space from the margin of the valve, and its centrally directed 

 convex half is divided uniformly by a well-marked, straight, and tapering line, 

 which represents the apex of the median lentelliptical area., the outlines of 

 which are defined in an exceedingly faint manner. A somewhat similar 

 arrangement in the structure at the wider extremity of the valves is met with 

 in Surirella saxonica, Auersw., S. robusta, Ehrenb. (=S. nobilis, W. Sm., 

 according to Grunow), S. bifrons, Kiitz., S. tenera, Greg. (=S. diaphana, Bleisch), 

 S. valida, A. S., S. rattrayi, A. S., but in all of these the reniform shape is 

 replaced by a more rounded or even by a bluntly triangular outline, the small 

 lenticular marginal space being either much reduced and rounded, as in some 

 varieties of & tenera, Greg., or concavo-convex, the concavity being directed 

 towards the margin, as in & valida, A. S. The infundibulate form of the 



