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9 
nature in other kind of shells, the latter being a movable apparatus 
for partially or wholly closing the aperture, and fully under the 
control of the animal inhabiting the shell. A unique arrange- 
ment found in the shell of a small land snail consisted of a 
movable door fixed by a tiny hinge fastened to the interior of the 
shell. In shape it was somewhat like the bowl of a spoon. The 
name given to it was the clausilium, and from that the family of 
those shells was called Clausilia. (A further illustration of 
peculiar formations of the interior of some shells was shown in 
specimens of rock borers dug out of the rocks and wood of the 
submerged forest at Bulverhythe). This particular formation was 
shaped like a sickle, and it served as a point to which the foot and 
viscera of the animal were attached. No other shells than those 
of the Pholas family had this object. 
Very few bivalve shells were without teeth. These teeth 
varied considerably in number. Some shells had but one or two, 
while one shown on the screen was stated to have nearly 270. A 
photo-micrograph of several of these teeth assisted the explanation 
of their form and use. A tough leather-like arrangement for 
holding the valves together and retaining them so that they can 
open and close with ease and exactitude; and the peculiar yet 
perfect arrangement of the muscles controlling the action of the 
valves as well as the movements of the animal within were then 
illustrated by written description thrown upon the screen in white 
letters. Having further dealt with several features of the internal 
economy of shells in general, the lecturer passed on to describe 
the external topography, pointing out the margins, the umbones, 
the spines, the ribs and ridges, the lines of growth, and the 
general plan of ornamentation of the shell, each and all of the 
features being illustrated by photographs of shells from the 
lecturer’s cabinet of specimens in the Hastings Museum. 
But it appeared that some molluscs had a shell formed within 
the body, the common Squid has a horny substance in the 
form of a gladius or pen; the Cuttle had, what was familiar to 
many people in the form of the well-known cuttle bone. (Of this 
object several interesting photo-micrographs showed the remark- 
able construction of different portions.) 
The common garden slugs also had either a small internal 
shelly plate or granules of calcareous substance, the formation of 
which was shown as seen under the microscope. 
At the present day about 25,000 different kinds of shells 
were known, and among them there was an enormous variety in 
size and shape as well as colouring. The Nautilus shell was 
shown as a type of one form ; the common whelk as another, and 
the scorpion shell as another. The beautiful cowries, beautiful 
in colouring and form, served as illustrations of the remarkable 
difference in the appearance of the shell of a young cowrie and 
that of the fully-grown or adult animal. The Haliotis or ear shell 
