Mr. Hogg on the Flustra arenosa. 319 



i This production is ranked by Ellis and Gmelin as a species 

 of the genus Flustra, which belongs to the order Vermes Zoophyta 

 of Linnaeus ; 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 7iidus 

 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 



