74 Transactions of the Boyal Microscopical Society. 



No tolerably good observer witb recent aj^pliances of immersion 

 lenses and condensers can fail to see the composite character of the 

 so-called costae, though there will be considerable variety of opinion 

 as to the most probable interpretation of the various aspects. 

 Tracing the beading on the median bands is, on the whole, much 

 more troublesome than exhibiting the composite character of the 

 costae, and it is probably on this point that most doubt will arise. 

 If, however, anyone with good tools and a suitable stock of 

 patience will go through a series of species, it will be readily 

 admitted that in some this medial beading cannot be denied, and 

 others may succeed in seeing it better than the writer has done in 

 the most difficult cases. 



The preceding observations have been made with a remarkably 

 fine immersion |^th by Powell and Lealand on their new system. 

 The condenser employed is a -r%ths one of Eoss, and the usual stop, 

 one radial slot, aperture lOQ"". The most serviceable eye-pieces 

 were C and D of Eoss' scale. 



Should these observations meet the eye of Colonel Dr. 

 Woodward, it may induce him to examine some of these diatoms, 

 and give microscopists the benefit of his very remarkable photo- 

 graphic skill. It would be impossible to make drawings that 

 would be accepted as satisfactory, until several good observers of 

 this troublesome class of object have compared notes and decided 

 which, out of many appearances, that look as if they corresponded 

 with fact, may be most prudently trusted. 



