AMMONITES Listen. 

 TAB. DL— Jig. 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.Derh,PL3b,f.S. 



1 HIS 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. 



