loyb YORKSHIRE TYPE AMMONITES— IT June 



107. AMMONITES GRACILIS, Simpson 

 (Plate CVII) 



Original Description 

 " [3°] d. A[mmonites] gracilis. [M. Simpson, 1843, p. 20.] 



" [I. Without a dorsal keel or furrow. 

 "a. No spines, p. 7."] 



" This has the general characters of A. communis ; but the whorls 

 are more slender and numerous, and the sides rather flatted. The radii 

 are more regular and better defined. It is from the upper Lias at Peak, 

 where it is rather plentiful. In examining a great many of these, 

 I generally found a chamber near the aperture, of great length, and 

 often hollow. This circumstance leads me to think, that it may still be 

 a distinct species ; and not the young of A. communis. 



Additional Details 



Simpson, 1855, p. 54, — " 57. A. gracilis, Simp. — Volutions 6, 

 exposed, slender, sides rather flatted ; radii regular, distinct, aperture 

 subquadrate ; diameter 3} inches. — Jet-rock, ILL. 



"These are found in masses, and are best distinguished by the 

 slenderness of the whorls. They are generally casts, and where the 

 shell remains, it is of a brown colour. In examining a great many of 

 these, I generally found a chamber near the aperture, of great length, 

 and often hollow." 



This description is placed under the following heading, 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." 



Simpson, 1884, 85, as 1855, but gives diameter as " three-quarters 

 of an inch." 



Remarks 



Proportions, 21, 26, 26, 51 ; subplaty-, subpachygyral, sub- 

 extremilatumbilicate. 



Stages, conch, serpenticone ; periphery, 1 ; ornament, 5. 



Whorls subquadrate, with flattened sides. Periphery slightly arched 

 and with a slight median elevation. Ribs distinct, mostly bifurcate, 

 occasionally entire ; small tubercle at junction ; secondaries with very 

 slight forward bend. 



Genus, Dactylioceras, Hyatt ; family, Dactyloidae, Hyatt. 



Result 



Dactylioceras gracile, Simpson sp. 1843, Whitbian, exaratum 

 zone, Peak, near Whitby. 





