4 A. A. MERLIN ON RESOLUTION OF AMPHIPLEURA PELLUCID A, ETC. 



meet with general acceptance until they receive confirmation at 

 abler hands than mine, nor indeed would it be desirable that 

 they should be so accepted, involving as they do important 

 theoretical considerations, until independent practical experience 

 shall have placed their truth beyond doubt. 



The subjoined notes on some of the forms lately examined 

 with the 4 mm, may be of interest. A very large central solid 

 cone has been invariably employed in conjunction with either 

 Gifford's or the beautiful new acetate of copper screen. 



Nitzschia curvula Sm. This diatom is mounted next to 

 Amphipleura pelhccida on Moller's dry " Probe-platte." Trans- 

 verse striae close and delicate, but undoubtedly resolved. 



Nitzschia sigmatella Grun. Moller's balsam type slide. 

 Transverse striae extremely faint and difficult, A delicate 

 object even with N.A. 1*3 and 1-4. 



Nitzschia linearis and N. ohtusa Sm. In balsam. The former 

 very faintly resolved into transverse striae, the latter not so 

 difficult. Dr. H. Van Heurck, in his " Synopsis des Diatomees," 

 gives iV. linearis as having 27 to 30 striae in O'Ol mm. 

 (25"399 mm. = l inch), and N. ohtusa 26 to 27 in O'Ol mm. 

 N. sigmatella Grun., is given at 25 to 26 striae in 0*01 mm., but 

 the specimen of this form on the type slide has much finer 

 structure than N. linearis and X. ohtusa. 



Nitzschia sigmoidea Sm. Moller's dry " Probe- platte " — 25^ to 

 26 striae in O'Ol mm. according to Van Heurck. This is remark- 

 ably easy with the 4 mm., the striae presenting a beaded appear- 

 ance. They can be certainly seen with the 1 2 mm. apochromat 

 of N.A. "65, so do not probably, in this instance, exceed 55,000 to 

 the inch. A specimen in balsam is also very easy with the 4 mm. 



Nitzschia sigma Sm. Van Heurck gives 22 striae in O'Ol mm. 

 Distinctly dotted in balsam, and very easy in mixed mono- 

 bromide of naphthaline and balsam. 



/ 



Grammatojjhora oceanica Ehrbg. = G. suhtilissima. Moller's 

 dry " Probe -platte." Resolved into transverse striae. Van 



