BARKER, ON A NEW MICROSCOPIC GROWING-STAGE, 11 
The diatoms of this genus in consequence of their forms 
present when mounted their fronts as frequently as their 
sides, as may be seen by reference to any slides containing 
specimens of the genus. 
Amphiprore are tolerably plentiful, they much resemble 
the frustules of Donkinia in their front aspects, as may be 
seen by reference to the diagrams, but their side views closely 
resemble the common Navicule, the exception being that in 
the Naviculz the median lines are in or near the middle of 
the frustules, while in the Amphiprore the median lines form 
double curves in close contiguity to one of the sides. 
The whole of the genera just referred to are marked by 
striz of greater or lesser fineness ; some are so coarsely striated 
that the lines are visible by means of a lens of low power, say 
2rds of an inch, and others are so delicately and closely 
striated that the strie are only resolvable by the highest 
microscopical power and the most perfect illumination. 
Many of the Pleurosigmata, such for example as mari- 
num, nubecula, and obtusum, are coarse; lanceolatum and 
fasciola are fine ; prolongatum and arcuatum are, with a Ross’ 
4th, achromatic condenser, and central or other stop, difficult 
of resolution, and spectrosum, a new diatom I am unable to 
resolve. 
The strize of the Toxonidea, are all double oblique ; on the 
Pleurosigmata they are double oblique, transverse, and 
longitudinal; on the Donkinie they are the same; on Amphi- 
prora alata the strie are transyerse, but on Amphiprora 
duplex they are absent or invisible to the power at my,;command. 
The lines on local marine diatomacee vary from 10,000 to 
80,000 in an inch, and they form admirable tests for the 
higher powers of microscopes. The celebrated test object of 
a few years ago, Pleurosigma angulatum, is now exceeded by 
the more delicate strie of Pléurosigma lanceolatum, Toxon- 
idea insignis, Donkinia carinatum, and Pleurosigma arcu- 
atum. 
A New Microscoric GrowinG STAGE. 
By Joun Barker, M.D. University of Dublin. 
(Exhibited at the Dublin Microscopical Club.) 
THE advantages of some contrivances for facilitating the 
examination of objects from time without disturbance, and 
which could be kept as nearly as possible under the same con- 
ditions under which they were first observed, has at all times 
been a desideratum in microscopic science ; and the pages of 
