ON GASTEROPODA. 367 
2. That they also employed a species of buccinum, which 
was smaller, to obtain an analogous, though a little different 
colour, and this species is probably the B. lapillus of 
Linneus. 
3. That it is certain that a great number of species of this 
family furnish an analogous liquor; but it is probable that 
they do not all do so. 
4, That it is even probable that all the individuals of the 
same species do not produce it. It is a query whether this 
depend on sex, or age, or the epoch of reproduction ? 
5. That we do not precisely know in what part of the 
animal this matter is found. Is it in the depurating organ, or 
in the generative apparatus? We might be induced to believe 
in the latter, as the eggs of the B. lapillus contain the same 
liquor in abundance. 
6. That the process employed by the ancients in dyeing 
purple is as yet unknown. 
7. That the chemical phenomena of the purpurification are 
as yet but very incompletely known. 
We shall now pass at once to the last order of the gastero- 
pods, the Cyclobranchia, on which we can afford but very 
little space. 
The PATELL#& are animals much more simply organized 
than the preceding mollusca. They live upon the shores of 
the sea, and constantly on those parts which are alternately 
covered and left dry by the waters. None are yet known 
belonging to the fresh water, nor have any been observed even 
in the mouths of large rivers. They are almost constantly 
fixed upon rocks and submerged bodies, and sometimes in 
excavations tolerably deep, which they have hollowed in the 
substance of the rock. They do not, however, always remain 
in the same place, as some persons have supposed. It is 
now a long time since Reaumur published his observations on 
their mode of locomotion. It takes place in the same way as 
