70 
NATURAL HISTORY. [UPPER FLOOR. 
formed of concentric rings. The young of the former are 
born alive, being then covered with bands of cilia. Then fol¬ 
low the Foolscap Limpet, ( Capulus ,) which is attached, by 
the back of its foot, to shells and other marine bodies, on 
which it forms a smooth disc, either by dissolving the sur¬ 
face, or by depositing on it a shelly plate. Lastly, succeed 
the genera Velutina , Crepidula, and Calyptrea which have 
no opercula. The branchiae of the animals of the last 
two genera are formed of long filiform processes, placed 
at a very oblique angle across the back of the neck. 
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 . 
Case 5 contains the shells of those animals which have 
their branchiae placed on the side of their back, under a 
kind of lid, as the Bulla and Bullcea, -which have the body 
divided into two portions, and no tentacula, Some of the 
animals are very voracious, and prey on shell-fish> for which 
purpose they are furnished with a gizzard covered with 
three shelly plates, by which they can crack the shells in 
the stomach, after having swallowed them whole. Others, 
as the Aplysia , have tentacula; and emit a great quantity 
of a purple fluid. In this Case are also the shells of those 
animals which have their branchiae placed on the right 
side, in a groove between the body and the foot, as the 
Pleurobranclius ; and lastly, those in which the branchiae 
are placed along both sides on the inner edge of the man¬ 
tle, as the Patella , which has a simple conical shell, with 
its apex bent toward the head of the animal, and Chiton , 
which has the body covered by a hard cartilaginous shield, 
into which eight valves, laid one over the other, like plate 
armour, are inserted. 
Cases 6 and 7 contain the shells of Mollusca.that breathe 
free air, for w 7 hich 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 ( Limax ), which 
have no shell or only a small internal one; the Tesiacellce, 
which have a small shell on the end of the body, and the 
Snails (Helix), Bulimus, Pupa,Clausilia, Succinea , and Vitri - 
