Mr. Hoce on the Flustra arenosa. 319 
This production is ranked by Ellis and Gmelin as a species 
of the genus Flustra, which belongs to the order Vermes Zoophyta 
of Linnæus ; although Ellis is uncertain whether it belongs to 
that genus or not; and Gmelin also appears to doubt whether it 
be a Flustra. Mr. Boys in vol. v. of the Trans. Linn. Soc. above 
quoted, states that he considered it undoubtedly to be the nidus 
of some marine animal, as he had found the cells entire, with 
eggs in each ; but later naturalists (Blainville perhaps alone ex- 
cepted) do not agree with him in this opinion. 
The shape of this substance is curious; it greatly resembles 
the hoof of a colt, and is about equal in thickness to the peel of 
an apple or of an orange. - ! 
It is composed of fine particles of sand, cemented by animal 
gluten, and forms a crustaceous substance of a semicircular 
shape, very friable when dry. If a piece be held to the light, it 
will appear full of circular cells, which are in some degree trans- 
parent, and placed nearly in a quincunx order. Upon opening 
the cells, I discovered in each, one or two minute testaceous 
bodies of a yellowish colour, which are transparent and very 
brittle. In the interior of these I further observed an orange 
spot, darker than the rest of the shell, and which I conjectured 
to be the dead animal belonging to the shell. 
In order to ascertain more accurately the nature of this sub- 
stance, and of the small shells I had observed in the dry speci- 
men, I procured fresh from the sea on the coast of Durham, where 
it abounds, a piece, which I placed immediately in a glass of 
sea-water, and changed the water occasionally. A few days 
after, the embryo shells hatched; I examined them with a micro- 
scope, and found that they bore a perfect resemblance to the 
young shells of the livid Nerite (Nerita glaucina of Linn.). The 
animal contained in each was white, and had two very minute 
black 
