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mencement appears to grow uniformly and regularly around 
the margin of the larval shell, and thus at once becomes a 
complete cone, while in P. pellucida the growth is at first 
entirely on one side, forming as it were a very large and 
expanded outer lip. I refer the present shell, though without 
positive proof, to Acmcea virginea. The fourth limpet-like 
shell is quite different from those already mentioned, it forms 
a more depressed cone, and is strong, with a translucent flinty 
texture, and the surface is marked with numerous fine, equal, 
radiating ribs. There is no deciduous cap, but the apex of 
the cone is a little flattened and presents a circular area, 
which is smooth and glassy, and appears as though a small 
transparent button were sunk into the substance of the 
shell. 
The occurrence of the shells of fry of great numbers of 
species both of univalve and bivalve mollusca in the sample of 
sand from Dogs Bay which I am examining, has led me to 
attempt their identification with the view of obtaining inform- 
ation as to the characters of some of the larval, or more 
properly speaking foetal, forms, which have not hitherto been 
observed. In this inquiry it is necessary to give a more 
definite meaning to the term u Fry” than has generally been 
done, for it appears to have been used indifferently for the 
foetal shell as it comes from the egg, and for the young which 
has grown considerably beyond that condition. Shells of the 
latter kind still show the foetal shell perfectly, and at the same 
time display characters in the aftergrowth by which at all 
events the genus, and in some cases the species may be 
determined, and it is specimens with these double characters 
that I shall distinguish as fry. At present I will leave 
the microscopic univalve shells without further notice, except- 
ing to remark that, while as a rule all foetal shells are smooth 
and glassy, there are among the univalves some striking 
exceptions, where the shell is beautifully sculptured, as in 
