ii5b YORKSHIRE TYPE AMMONITES— II July 



115. AMMONITES RUGOSUS, Leckenby 

 (Plate CXV) 



Original Description 

 [Leckenby, 1859, PP- 7» 9] 



" [P. 7.] Fossils of the Kelloway Rock of Yorkshire .... 

 Ammonites rugosus, Leckenby. 



" [P- 9] 3- Ammonites rugosus, Leckenby. 



" Gibbous, deeply umbilicated, ribs very thick and strong, separated 

 by wider spaces. Aperture rounded, indented one-fourth by the suc- 

 ceeding whorl. 



" Locality. Near Gristhorpe Bay." 



Remarks 



Proportions, 66, 45, 66, 22, Perplaty-, subextremipachygyral ; 

 subangustumbilicate. 



Stages, conch, sphaerocone ; periphery, 1 ; ornament, 4(c). 



The umbilicus is deep, narrow, gradate ; the umbilical wall is high, 

 almost perpendicular, smooth with definite edge. Ribs commence on 

 this edge, where they are sometimes connate : they increase in strength 

 as they progress to middle of periphery. The periphery is not defined, and 

 may be said to extend as an arch from one umbilical edge to the other ; 

 the greatest thickness being just on umbilical edge. Suture-lines obscurely 

 shown. The principal feature is the very wide ES (foreshortened in 

 photograph), so that L 1 is situated at about J of distance from inner 

 margin, while L 2 is nearly on margin. 



Genus, Pachyceras, Bayle 1878, close ally of Erymnoceras, Hyatt 

 (A. coronatus) ; family Pachyceratidae, now p. xiii. 



Geological position : from a hard grey, somewhat sparingly oolitic, 

 calcareous matrix. R. Douville (1912, p. 10) says Pachyceras characterises 

 the beds H. 1-3 of Vrllers-sur-Mer, Normandy, with Peltoceras athletoides 

 and first appearance of Quenstedticeras. S. Buckman (Q.J.G.S. 1913, 

 LXIX, 153) placed this species, from its matrix, somewhat higher — with 

 verttimnus. Possibly it marks a separate zone — post-renggeri--pre- 

 vertumnus. 



Result 

 Pachyceras rugosum, Leckenby sp., Divesian [pre- verttimnus 

 (Pachyceras) zone], near Gristhorpe Bay, near Scarborough, Yorkshire. 



