83b YORKSHIRE TYPE AMMONITES— II August 



83. AMMONITES VALIDUS, Simpson 

 (Plate LXXXIII) 



Original Description 

 " 86. A[mmonites] validus. [M. Simpson, 1855, pp. 62, 63.] 



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

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



" Volutions 6, exposed, outer whorl [p. 63] J the diameter ; radii 

 strong, coarse, annular, wider than the intervening spaces, split in two 

 or three on the back, armed with a row of broad tubercles on the outer 

 margin of the whorls ; aperture circular ; diameter 3 J inches. 



" This is a much coarser ammonite than the last [A. retusus], with 

 fewer whorls, and stronger radii, which become almost obsolete towards 

 the aperture ; there are the same large flat scars of the tubercles, and 

 the ramifications of the septa are the same. It appears to be from the 

 same beds of lower lias. — Mr. Leckenby's Col." 



Additional Details 



Simpson, 1884, 95, adds to end of first par. " L.L., y [y], R.H. Bay" ; 

 omits " Mr. Leckenby's Col." 



Remarks 



Proportions, 83, 31, 32, 46 ; subplaty-, subpachygyral, perlatum- 

 bilicate. 



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

 remain only the scars from where the septate spines have been removed. 

 The tubercles begin at about 10 mm. diameter, being preceded by ribs, 

 and, perhaps, a short smooth stage. 



Genus, Deroceras, Hyatt ; family Deroceratidae. 



Simpson noted correctly the differences between this species and 

 his A. retusus (No. 82) : there are more whorls to that species, the 

 coiling being slower in the young stage, while the costae develop slowly 

 and feebly for a long time. It may be that A. retusus is an example of 

 A . validus with cunctative palingenesis ; but it has also a flatter venter, 

 and the spinous stage, when attained, is not so strongly regular. 



Restdt 

 Deroceras validum, Simpson sp. 1855, Charmouthian, armatum 

 zone, Robin Hood's Bay, near Whitby. 



