rosb YORKSHIRE TYPE AMMONITES— II June 



105. AMMONITES MUTATUS, Simpson 

 (Plate CV) 



Original Description • 



" 88. A[mmonites] mutatus. [M. Simpson, 1855, pp. 63, 64.] 



[I. Without a dorsal keel or furrow." p. 35. 

 b. Armed with spines or distinct tubercles, p. 58.] 



" [P. 63] Volutions 6, inner ones J concealed, outer whorl J the 

 diameter ; radii on the inner whorls strong, obtuse, ending in a distinct 

 knob or tubercle, on part of the outer whorl numerous, fine, irregular, 

 annular ; aperture an ellipse ; diameter 1 inch and eight-tenths. 



" [P. 64] This is a smooth, neat ammonite of a greyish colour. 

 Several of the radii on the inner whorls have a slight groove, running 

 into the knobs ; in some places the grooves go past the knobs, and form 

 additional radii, without knobs ; the radii on the outer part of the outer 

 whorl, in places, are little more than annular striae, and the tubercles 

 become obsolete. It appears to be from the lower lias. — Mr. Clarkson's 

 Col." 



Simpson, 1884, 96, typographic alterations only. 



Remarks 



Proportions, 46, 36, 26 ? 47 ; platy-subpachygyral, perlatum- 

 bilicate. 



Stages, conch, serpenticone ; periphery, 1 ; ornament, 5 to 3c, 

 rapid decline. 



There is a regular coronet of spines to 31 mm. diameter ; then rather 

 sudden loss. The tubercled whorls are obtrapeziform ; the costate whorl 

 elliptical. The peripheral view is imperfect owing to damage on one side. 



Genus, Deroceras, Hyatt ; family Deroceratidae. 



Geological position presumably Simpson's L.L.y. 



Result 

 Deroceras mutatum, Simpson sp. 1855, Charmouthian, [armatum 

 zone, near Whitby]. 



