63b YORKSHIRE TYPE AMMONITES Oct. 



63. AMMONITES ANNULIFERUS, Simpson 

 (Plate LXIII) 



Original Description 

 " 53. A[mmonites] annuliferus. [M. Simpson, 1855, p. 50.] 



[" The following species, to the end of the Section, have all a family 

 resemblance to A. communis : — 



" Whorls narrow, exposed, with numerous slender, annular ribs, 

 which generally split in two on the back." p. 50.] 



" Radii obtuse, on the outer whorl separated by narrow grooves, 

 split in two, then pass straight over the back, where they are nearly 

 obsolete ; aperture an ellipse, indented by the succeeding whorl." 



Simpson, 1884, 81, the same. 



Remarks 



Stages, conch, serpenticone ; periphery, i ; ornament, 5 to 4c. 



The whorls are rounded ; the periphery arched ; the umbilicus open 

 with gibbous steps ; the ornament is a tuberculate stage up to about 

 17 mm. diameter, with occasional fibulation ; after that, ordinary bifurcate 

 costation, costae septate. 



The species shews catagenetic ornament of the Dactylioceras pattern 

 following after fibulate tuberculation. The species is therefore a 

 degenerate derivative of Peronoceras or Porpoceras, the fineness of the 

 ornament perhaps indicates the former. Therefore genus Peronoceras ? 

 Hyatt, (Gen. v) ; family Dactyloidse. Nothing is said about its 

 geological position, but it is presumably from the Alum Shale. 



Result 



Peronoceras ? annuliferum, Simpson sp. 1855, Whitbian, [fibu- 

 latum zone ? near Whitby]. 



