ROOM XII. 
Nat. Hist. 
82 
cesses, placed at a very oblique angle across the back 
of the neck. 
In the end of the Table are placed the shells of 
animals which greatly resemble the former in the form 
of their branchiae, but differ in having a fringe on 
each side of their body, as the genera Trochus, Mo - 
nodonta and Haliotis . These have a pearly appear¬ 
ance on the inner surface: the two former are fur¬ 
nished with spiral opercula, and the latter is provided 
with a series of holes, by which the water is intro¬ 
duced into the branchiae. The genera Fissurella and 
Emarginula, are not pearly, but the former has a hole 
near the apex, and the other in the front margin of the 
shell, for the passage of the water to the branchiae, 
and the expulsion of the faeces. And lastly the genus 
Lottia , which has a shell exactly like Patella in shape, 
while the animal very nearly resembles those of the 
two latter genera, except that it has only one branchia 
placed obliquely across the back of the neck, which 
is exerted when the animal walks. The larger species 
of these animals are eaten, and also used as bait. 
The eggs of some, as the Neritce , are ovate, covered 
with a horny skin and attached to other shells, and 
those of the Naticce have been described as a coral 
under the name of Flustra arenaria. 
Cases 5 and 6 contain the shells of Mollusca that 
breathe free air, for which purpose they are furnished 
with a cavity over the back of the neck, which cavity 
is internally lined with a quantity of vessels. Those 
which live on land, have cylindrical, retractile tentacula, 
as the Slugs (. Limaco ), which have no shell or only 
a small internal one ; the Testacellce , which have a 
small shell on the end of the body, and the Snails 
(. Helioc ), Bulimics, Pupa , Clausilia, Succinea and 
Vitrina , which have large shells, differing from each 
other in form. The animals of the last two genera 
are so large, as scarcely to admit of their being with¬ 
drawn into their shells, and that of the last has a fleshy 
collar 
