62b YORKSHIRE TYPE AMMONITES Oct. 



62. AMMONITES CRASSIUSCULOSUS, Simpson 

 (Plate LXII) 



Original Description 

 " 68. A[mmonites] crassiusculosus. [M. Simpson, 1855, p. 57.] 



[" 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. ] 



" Thickish ; volutions 6 or 7, outer whorl J the diameter, neatly 

 rounded ; radii strong, prominent, obtuse, split in two on the back ; 

 aperture transverse ; diameter ij inch 



" This is a very neat and slender species or variety, intermediate 

 between A. crassus and A. crassulus. It is from the jet-rock of the lias. 

 There is another in the same beds, which resembles it in the slenderness 

 of the whorls, but the aperture is circular." 



Simpson, 1884, 88, 89, the same. 



Remarks 



Stages, conch, serpenticone ; periphery, i ; ornament, 4 (4c ?). 

 Whorls depressed, sides rounded, periphery flatly arched ; umbilicus 

 open, convexigradate ; ornament very regular, costation bifurcate, 

 secondary ribs with slight forward bend on periphery. 



Genus, Dactylioceras, Hyatt ; family Dactyloidse. 



Result 

 Dactylioceras crassiusculosum, Simpson sp. 1855, Whitbian, 

 exaratum zone, near Whitby. 



