114 Professor Smith's Conspectus of the Diatomaeese. 



The beading here described is very distinctly visible, with my 

 aplanatic searcher and a quarter objective. 



The spurious spines of the Lepisma tfaccharina ought to 

 be seen, as Mr. Wenham described the Podura " note of admiration" 

 markings " with that distinctness and sharpness of definition that 

 so delights the eye of the optician."* Both the Lepisma and 

 Podura scales are formed of beaded striae crossing at a variable 

 angle. The optician ought, therefore, to delight in the note of 

 a 'miration markings developed in (Fig. 3), shown by one of the 

 best objectives now made when incorrectly adjusted. 



The study of spurious appearances under the use of a variety 

 of objectives of high and low degrees of excellence, is one of the most 

 instructive subjects of microscopic research. Notwithstanding that 

 the famous Podura mark so delights the eye of the optician, a 

 more profound resolution dissipates this spurious appearance, as 

 well as the false beads of Fig. 1, and the quasi Podura " notes" 

 of Figs. 2 and 3. 



It is very easy to produce the false appearance of scattered 

 spherules somewhat similar to Fig. 1 in the Podura as described 

 by Mr. Wenham. 



VI. — Professor Smith's Conspectus of the Diatomacefe. 



By Captain Fred. H. Lang, Presidents the Reading 

 Microscopical Society. 



The study of the Diatomacese, instead of becoming easier, is getting 

 more difficult every year, simply because new genera are constantly 

 being added, on most insufficient grounds, to the ever-lengthening 

 list, and because there is no one authority on the subject. Ehren- 

 berg, Rabenhorst, Kutzing, W. Smith, Ralfs, Arnott, Brebisson, 

 Donkin, Kitton, and a host of others, besides Dr. Pfitzer, who has 

 just published a new classification based on the method of repro- 

 duction of the frustules, are all more or less authorities; but to 

 whom are we to trust ? And now Professor H. L. Smith has pub- 

 lished in the American Microscopical Journal, the ' Lens,' his 

 Conspectus of the Diatomacese, which, at all events, appears an 

 effort in the right direction to reduce within a reasonable number 

 of genera the vast variety of forms in this most prolific and mul- 

 tifarious order. 



Probably any classification of these curiously-beautiful and 

 interesting organisms must for the present be more or less artificial ; 

 his is certainly completely so, as he himself allows, based as it is en- 

 tirely on the tout ensemble and general form and appearance of the 



* Page 124, vol. ii., ' Microscopical Journal.' 





