R. P. Whitfield— Carboniferous air-breathing Mollusk. 127 
In making the studies of the afore-mentioned shell, [ obtained 
from John Collette, Esq., State Geologist of Indiana, specimens 
of Pupa Vermilionensis and Dawsonella Meeki Bradley. I find 
that the latter shell has the aperture much contracted by the 
thickening of the lip on the inside, and against the body volu- 
tion by a thickened callus coating the volution and almost 
concealing the umbilicus, while it straightens that margin of 
the aperture. These features contract the aperture to a very 
small part of what it must have been before the callosity was 
formed, while the surface of the callus is slightly concave from 
side to side, over the distance between the umbilicus and the 
margin of the aperture. The form of this callus, especially when 
taken in connection with the thickening of the inside of the 
lip, has so much resemblance to the corresponding parts of 
Helicina, that I cannot but come to the conclusion that Daw- 
sonella was an operculated shell, although in the rock in which 
they are found I have sought in vain for anything resembling 
an operculum. In the article quoted above, the author shows 
the extent of this callus in his figure 18 on page 412, and it is 
well shown in the accompanying outlines. 
5. 6. 
Sir 
ce 
Dawsonella Meeki Bradley. 
Figs. 5 and 6, profile and basal view of Dawsonella Meeki Brad., to show the 
form of aperture and callus resembling that of Helicina. ‘ 
some foreign body ; and they have, I presume, been attached 
