SILURIAN FAUNAS. 247 
which are plane above, with a broad umbilicus below, in which all 
of the volutions are probably visible. In cross-section the yolutions 
are subeircular. 
LOXONEMA? sp. undet. 
Plate XXII., Figs. 9-11. 
One or more species of coiled shells, with elevated spires, are present 
in the lower beds of the Decker Ferry formation. These are all im 
perfect casts, and preserve no characters by which they may be referred 
to their proper genera. They may be placed provisionally in Loxo- 
nema, 
PLATYCERAS sp. undet. 
Plate XXII., Figs. 12-13. 
Description.—Several specimens of what appears to be a small 
species of Platyceras or Platyostoma have been observed in the lower 
beds of the Decker Fery formation. As nearly as can be determined 
they have about two contiguous yolutions, the inner one being very 
small and the outer one expanding rapidly to the aperture, which is 
relatively large. In cross-section the volutions are suboval or sub- 
ebliptical in outline. The upper surface of the volutions lies in a 
plane. 
The dimensions of the most perfect specimen are: diameter, 11 
mm.; height of aperture, 8.5 mm. 
Remarks.—All the specimens of this little shell which have been 
observed are imperfectly preserved. One which resembles the re- 
mainder in other respects has a sharply carimate periphery, and conse- 
quently the cross-section of the volutions is subtriangular. It is not 
possible to determine from the specimen whether this variation is 
normal or whether it is produced by a distortion of the shell. 
