57b YORKSHIRE TYPE AMMONITES May 



57. AMMONITES ANDREI, Simpson 

 (Plate LVII) 



Original Description 

 36. A[mmonites] Andrsei. [M. Simpson, 1843, p. 23.] 



[" I. Without a dorsal keel or furrow, p. 7. 

 " b. Armed with spines or distinct tubercles." p. 22.] 



" This has nearly the same characters as A. fibulatus ; but the ribs 

 are not in the button and loop style. Each rib has a knob near the back, 

 then splits into two or three. It has been named after Mr. Thos. Andrew, 

 a respectable dealer in fossils in this town." 



Additional Details 



Simpson, 1855, 59. — " 76. A. andre/E, Simp. — Volutions 6 or 7, 

 exposed, outer whorl nearly J the diameter ; radii numerous, prominent, 

 form knobs near the outer margin of the whorls, then spHt into 2 or 3 

 on the back ; aperture subquadrate ; diameter 2J inches. 



" Towards the aperture, alternate radii are introduced, without 

 knobs, and at length the knobs become entirely obsolete. — U.L." 



Simpson, 1884, 91, similar. 



Remarks 



Stages, conch, serpenticone ; periphery, i ; ornament, 5*. 



Spite of Simpson's assertion, there is a button & loop (fibulate) 

 pattern till about 40 mm. diameter. After that, plain tuberculate 

 pattern. The subsequent failure of knobs is perhaps due to an injury, 

 of which there are signs. The secondary ribs have a slight forward sweep 

 over a flatfish arched periphery. 



Genus, Porpoceras (Gen. p. v) ', family, Dactyloidas, Hyatt. 

 Geological position, presumably Alum Shale. 



Result 



PoRPORCERAS ANDR.«i, SiMPSON sp. 1843, Whitbian [fibulatum zone, 

 near Whitby]. 



