HENDllY, ON AMPHIPLEURA PELLUCIDA. 8 



I have never used the -J^th or -j'^th inch objectives, or any ac- 

 cessory apparatus, I deem sucli of no utility for the object of 

 the present research. 



In surveying a slide for the more shallow or difficult mark- 

 ings, almost every shell lying in a proper position should be 

 carefully examined with an Ath or -^^'^h. inch objective, and 

 B eye-piece ; and when indications are observed, then all at- 

 tention, both to direction and precise focus, must be paid; 

 which will not unfrequently open out a striation when not 

 expected, and which is far from illusory ; for with such latter 

 appearances I do not, for my own part, profess to deal, 

 leaving others to answer for themselves, in reply to Messrs. 

 Sullivant and Wormley. 



I believe there is yet much to overcome in the preparation 

 (boiling, &c.) and mounting of slides. The observer should 

 not trust too much to the apparent beauty of his slide, nor yet 

 suppose that because of the great brilliancy of a coarser 

 diatom, the finer should be necessarily resolved, if re- 

 solvable at all ; such a result does not ahvays follow in practice, 

 for the vapours of asphalt, siliceous precipitation, altered 

 refraction, and other causes, yet unknown, may possibly 

 interfere to foil every efibrt in observation. 



I am fully satisfied as to the ready resolution of the true 

 strise of Amphipleura j^elhicida, and in the several slides 

 above referred to can bring out fifty other shells when re- 

 quired. I am equally satisfied that Amphipleura jjellucida 

 presents, in opposition to Messrs. Sullivant and Wormley^s 

 views, a wide numerical value in striation, in common with 

 some other diatoms, as Nitzschia sigmoidea, for example ; 

 and Avere I to abandon these views, I should be at once ready 

 to account the indications of the microscope for the most 

 part fallacious ; believing, however, that these views, honestly 

 set forth, will be ultimately confirmed and adopted. 



