Stiles: Oolitic Limestone. 63 
difference between this and Ketton ; the granules are smaller, 
the cementation much more perfect, and the stone is con- 
sequently denser, and I should say more durable. 
PHOTOGRAPHIC DETAILS. 
* Objective.-—2 inches without eye-piece, stopped down by 
the insertion of a diaphragm with a small central aperture at 
the back of O.G. 
Magnification.—12 diameters in all cases. 
Plate.—Wlford Chromatic. 
Developer.—Rodinal I in 24. , 
Exposure.—5 minutes. 
Illumination.—Paraffin lamp, flat flame, parallelised by 
a 2 inch double convex Jens on to the concave mirror mounted 
above the objective and thence reflected on the object with as. 
little obliquity as possible. In this way deep contrasts are 
avoided, and a softer and more natural appearance thereby 
secured. 
Camera.—A horizontal one, with the illuminating apparatus 
raised sufficiently for the beam of light to clear the stage and 
reach the mirror. 
N.B.—The Photographs have been reproduced on a smaller 
scale in the blocks (8 diameters), and are not so clear as the 
originals. To anyone particularly interested I shall be glad to 
send the originals for inspection, as well as the stereogram. 
20% 
ARACHNIDA. 
New and Scarce British Arachnida.—Dr. C. F. George 
has kindly presented the following mites, recently figured 
in The Naturalist, to the Hull Museum, and this record is 
made so that students of the arachnida will know where the 
originals can be referred to:— Trombidium musham, T. 
bicolor, T. buccinator, Johnstoniana levipes, Ottonia ignota, 
O. sheppardi, Rhagidia, Bryonia pratensis, Ammonia (Cyta), 
Bdella histrionum, Ba. hexophthalma, Bdella spp. and larva, 
and larve, nymph, adult, and dissected details of Ruitteria 
nemorum. Some of these are the type specimens. They 
are all mounted as microscopical preparations. A previous 
gift of a similar nature was recorded in this journal for Novem- 
ber, 1911, p. 372.—T.S. 
* In taking the Stereogram, the aperture of the diaphragm was 
ex-centric, its position being reversed for the second exposure. These 
exposures were made on two plates 3} in. x 2} in., and care was taken 
that the illumination, exposures, developement and subsequent treatment 
were identical. 
1915 Feb. 1. 
