79 
I am not acquainted with the habitats of either of these two last 
mentioned fossils ; but imagine, from the appearance of the matrix, 
that they are from the neighbourhood of Dudley, in Worcestershire. 
XLI. Cyclostoma. A discoidal or convexo-conical, nearly trans- 
parent univalve, with cylindraceous turns. The opening round, with 
a circularly continued margin, suddenly and widely thrown back. 
The eyclostomce, in their adult state, have their margins always re- 
flected, which is not the case with the delphinulce ; but they are more 
certainly distinguished from each other by the thinness of the shell of 
the eyclostomce, and by their never having any nacre, which is always 
possessed by the delphinulce. Cyclostoma spiruloides, Lam. is a minute 
species of this genus, the form of which may easily be comprehended 
without a figure ; since it is formed by three turns, spirally disposed, 
in the same manner as in the planorhcs: the last turn being so de- 
tached from the rest, as to give it the appearance of a young nautilus 
It must be observed, that there are some shells, not yet classed, whose 
openings are round, and whose margins are united like the eyclostomce ; 
but in which, unlike the eyclostomce, the margins are not dilated nor 
reflected, and which are of an elongated or turriculated form. 
Lamarck desci’ibes six fossil species : C. cornu pastoris, C. spiru- 
loides, C. planorhula, C. macrostoma, C. mumia, C. turritellata. 
XLII. Scalarici. A turreted univalve, with acute longitudinal 
raised ribs. The opening nearly circular ; the margins uninterrupted, 
bordered, and reflected. 
The raised ribs sufficiently distinguish the shells of this genus from 
those of delphinula and cyclostoma. 
I am not in possession of any fossil of this or of the two preceding- 
genera ; nor do I know of any having been found among our English 
fossils. Lamarck has discovered five species of this genus among the 
fossils of Grignon and Pernes : S. crispa, S. decussata, S. denudada, 
S. monocycla, and S plicata. 
