314 MICROSCOPY. 
Beck No. 3 eye-piece, power 7,000 times. With the ammoni- — 
sulphate of copper cell the longitudinal lines and dots are dis- — 
played with ease. 
This is one of the most difficult test diatoms thus far studied, — 
ranking but little easier than A. pellucida, N. crassinervis and 
Nitzschia curvula. OE 
Amphipleura pellucida.—Many times the writer has been able — | 
to confirm the observations of longitudinal lines on this most 
difficult test shell, but never has succeeded in seeing the dots ex- _ 
cept with the blue cell and Wenham’s paraboloid, and only then 
under favorable circumstances. (See I. E. Smith, in “The 
Lens,” April, 1873, page 115. See also the Naruratist, May, 
1873, page 316.) When resolution is effected, the dots are ex 
ceedingly minute and uniform in size, showing as mere points of : 
light when magnified 2500 times. On one occasion the writer has ; 
seen fine dark lines crossing between the transverse striæ like j a 
steps of a ladder, the dots or spaces plainly longest in direction 
parallel with the median line, proving the longitudinal to be finer 
than the transverse lines. oe 
One obstacle in the way of resolution of the longitudinal striæ 
is the presence of diffraction lines. The valves being so narrow — 
increases this difficulty. Only after much time is wasted, and 
after many discouraging failures, will tlie patient observer rece! 
the reward of success. 
Nitzschia curvula Sm.—The unusual number of spurious aP- 
pearances in this object leads me to suspect that it possesses ^ 
complicated structure as yet beyond the reach of the instru pre 
The extreme fineness of the longitudinal lines as compared 
the transverse reminds one of the Navicula cuspidata, and a8 
is the case with the coarser shell, no efforts avail to develo?” 
semblance of beading. 
Striatella unipunctata.—Two sets of fine lines, meee 
rection of the light is changed, may be made to exhibit a 
beads or squares. In point of value as a test will be found 
approach Surirella gemma. : eq the : 
Grammatophora.—Of this genus the writer has examin s 
G. marina, Q. subtilissima and G. serpentina ; all of which a 
solved into hexagons. Broken specimens of G. marina shon 
line of fracture running through the hexagonal planes and 
points of the net-work projecting. The markings contin 7 
