49b YORKSHIRE TYPE AMMONITES Feb. 



40. AMMONITES CEREUS, Simpson 

 (Plate XLIX) 



Original Description 

 " 42. A[mmonites] cereus. [M. Simpson, 1855, p. 47.] 



\" I. Without a dorsal keel or furrow. 



" a. No spines." p. 35.] 



" Volutions 6, exposed, outer whorl nearly |- the diameter ; radii 

 very prominent on the sides, nearly obsolete on the back, separated 

 by rather wide concave spaces ; aperture ovate, transverse ; diameter 

 nine-tenths inch. 



" Shell smooth and bright, with a few striae, colour light-brown. 

 L.L. ; Mr. Ripley's Col. 



A dditio nal Details 



Simpson, 1884, 77, adds " of an " after " nine-tenths " ; adds " R.H. 

 Bay " after " L.L." ; omits " Mr. Ripley's Col." 



Remarks 



Stages, conch, serjienticone ; periphery, i ; ornament, 4. 



There is a certain likenass in this species to costate Xipheroceras : 

 but the suture line negatives the association : it points to connection 

 with the .4. raricostatus series, in which absence of a keel is a primitive 

 feature. 



Genus Echioceras, Bayle, 1878. Geological position uncertain. It is 

 not black like specimens of L.L. 13 ; it is not pyritized : it is of a 3'ellowisli 

 brown calcareous appearance (wax-like). 



Result 

 Echioceras cereum, Simpson sp. 1855, Sinemurian \ox\')io/um zone 

 or lower ?] Robin Hood's Bay, near Whitby. 



