1901] MICROSCOPICAL JOURNAL, — 391 
The subjoined notes on some of the forms lately ex- 
amined with the 4 mm. may beof interest. A very large 
central solid cone has been invariably employed in con- 
junction with either Gifford’s or the beautiful new acetate 
of copper screen. 
Nitzschia curvula Sm. This diatom is mounted next 
to Amphipleura pellucida. 
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. ibbisees Sm. Inbalsam.. The 
former very faintly resolved into transverse striae, the 
latter not so difficult. Dr. H. Van Heurck, in his “Syn- 
opsis des Diatomees,” gives WN. linearis as having 27 to 30 
striae in 0°01 mm. (25-399 mm.—1 inch), and WV. obtusa : 
26 to27in 0-O0lmm. W. 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 WN. linearis 
and JW. obtusa. 
Nitzschia sigmoidea Sm. Moller’s dry “Probe-platte’’ 
—253 to 26 striae in 0:01 mm. according to Van Heurck. 
This is remarkably easy with the 4 mm., the striae pre- 
senting a beaded appearance. They can be certainly seen 
with the 12 mm. apochromat of N. A. ‘65, so do not prob- 
ably, in this instance, exceed 55,000 totheinch. A speci- 
men in balsam is also very easy with the 4 mm. 
Nitzschia sigma Sm. Van Heurck gives 22 striae in 
001 mm. Distinctly dotted in balsam, and very easy in 
‘mixed monobromide of naphthaline and balsam. 
Grammatophora oceanica EKhrenbg.— G. subtilissima, 
Moller’s dry “Probe-platte.” Resolved into transverse 
striae. Van Heurck gives 30 striae in 0:01 mm. for the 
G. oceanica var. indica Grun., and 30 to 31 for the G. 
oceanica var. novaezeelandiae Grun. Some specimens of 
G. subtilissima, however, are finer, running at about 88, 
000 to the inch. 
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