'/)b YORKSHIRE TYPE AMMONITES Apr. 



36. AMMONITES ARCTUS, Simpson 



Original Description 

 " 8. A[mmonites] arctus. [M. Simpson, 1843, p. 10.] 



[" I. Without a dorsal keel or furrow. 

 a. No spines " p. 7.] 



" This greatly resembles the last [A. dennyi] ; but the outer whorl 

 is narrower ; the back is rounded ; it has a few obscure annular radii, 

 but no constrictions ; it occurs along with the last." 



Simpson, 1855, p. 38 ; 1884, p. 66, the same. 



Remarks 



Stages, conch, serpenticone ; periphery, i ; ornament, 3c. There are 

 a few obscure ribs and a little irregularity which might indicate relics 

 of an auriculoid stage. The suture-Hne is goniatitic with few denticula- 

 tions. About I whorl is body chamber, the last two septa approximate. 



The specimen (figd. x 2) is presumably an immature Oxynoticeras, 

 Hyatt, in the larval or Cymbites stage of ornament and suture line, but 

 commencing to be serpenticone. Family Arietidae, Hyatt. 



Geological position, Ind. Band 13, with A. dennyi. The position 

 of A. dennyi was misprinted " Ind. Band 3 " in 7b, Ad. Details, line 3. 

 This should be corrected. 



Result 



Oxynoticeras arctum, Simpson sp. 1843, Sinemurian, oxynotum 

 zone, Robin Hood's Bay, near Whitby. 



