94 b YORKSHIRE TYPE AMMONITES— II Jan. 



94. AMMONITES SINUATUS, Simpson 

 (Plate XCIV) 



Original Description 

 83. A[mmonites] sinuatus. [M. Simpson, 1855, p. 62]. 



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

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



" Volutions exposed, outer whorl J the diameter, sides convex ; 

 radii obtuse, separated by rather wide concave spaces, commence on the 

 inner margin, slightly incline towards the aperture, and then in the 

 opposite direction form a row of tubercles on the outer margin, nearly 

 obsolete on the back ; aperture ovate or subquadrate ; diameter 4! inches. 

 — A Fragment, L.L." 



Additional Details 



Simpson, 1884, p. 94, places " , " after " opposite direction " ; 

 adds at end " R. H. Bay." 



Remarks 



Proportions, 114, 27, 26, 52 ; subplaty-, subpachy-gyral, sub- 

 ex tremilatumbilicate. 



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



This is a fragment of a body-chamber, but it is fairly well 

 characterized. The sides of the whorls divergent, venter flattish, aperture 

 obtrapeziform. 



The tubercles are quite small ; the lateral costse are small, sharp 

 and slightly sinuous, with intermediate lineations ; on the venter the 

 costae are subobsolete. 



Genus, Deroceras, Hyatt ; family Deroceratidse. The geological 

 position is not stated ; but the specimen is from an ironstone bed, pre- 

 sumably near the base of the Ironstone series. 



Result 



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

 zone], Robin Hood's Bay, near Whitby. 



