163 
AMMONITES Listen. 
TAB. DI. —fig. 1. 
Spec. Char. Subdiscoid, inner whorls partly con- 
cealed ; front convex, broad, crossed by nume- 
rous small ribs ; sides inversely conical, ribbed ; 
ribs terminated by tubercles. 
Syn. Conch. Naut. Ammonites Listeri. Martin, 
Pet. Derb. PL 35, /. 3. 
This elegant fossil is a miniature representation of 
A. Blagdeni (tab. 201) : its thickness almost equals its 
diameter, which seldom exceeds an inch and a half : at 
rather distant intervals annular depressions are to be 
observed upon the cast of the inside, which indicate that 
the edge of the aperture was thickened at certain periods 
of its growth. 
Martin says this shell is found in most of the Limestone 
tracts in his vicinity, particularly near Eyem and Middle- 
ton. We have received it from a stratum of Shale be- 
longing to the Coal series, and referred by Mr. Farey to 
his third Coal * : it occurs in nodules of either Limestone 
or Iron-pyrites. In the latter substance it often happens 
that only casts of the outside remain, consisting of two 
spirally ornamented cones placed with their apices near- 
ly in contact : such are represented in British Mineralogy 
(tab. 455), and probably came from Whitley-wood mine 
near Sheffield. The specimens now figured are those 
See Derbyshire Report, p. 214. 
