CYPK/EA. 
83 
in the construction of the Univalves, the whorls 
increase in magnitude as they advance transversely 
from the apex, and receive no increment after the 
perfect aperture is formed. This bespeaks a limit 
in the growth of the inhabitant, at which he is 
taught by instinct to finish off his work. If, there- 
fore, for any reason, upon which from ignorance 
we cannot argue, these slugs do quit their shells, 
it is not, surely, on account of an anomalous ex- 
cess of bulk. A remark which has been made bi 
«/ 
the author, whether justly or not will hereafter be 
decided, would seem to favour a very opposite 
opinion. In numberless specimens of the Cyprsea 
exanthema which he has inspected, the thinner and 
obviously younger shells were, with few exceptions, 
of large dimensions, whereas the fully ocellated 
and thicker individuals were considerably smaller. 
So much difference is there usually in size, that 
they might be considered as two distinct varieties, 
were not a progressive course easily obtained, from 
those having broad bands alone, to those covered 
with white spots, and totally destitute of bands. 
This course, however, follows an inverse law with 
regard to magnitude. The above remark is simply 
