g8b YORKSHIRE TYPE AMMONITES—II Mar. 



98. AMMONITES HYPERBOLICUS, Simpson-Leckenby 

 (Plates XCVIIIa, b.) 



Original Description 



[Leckenby, 1859, PP- 7> 1J > 12 > x 5-] 



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



" Am. hyperbolicus, Simpson, MS. 



" [P. 11.] 24. Ammonites Chamusseti, D'Orbigny 



" Ammonites lenticularis , Phillips 

 " Locality. Red Cliff only. 



" 25. Ammonites funiferus, Phillips. 



" This is a much more depressed species than Am. Chamusseti, and 

 the intricate character of the foliations of the septa also distinguish it. 

 " Locality. Red Cliff only. 



" [P. 12.] 26. Ammonites hyperbolicus, Leckenby (Simpson MS.). 



PI. II, fig. 4*. 46. 



" This, on the contrary, is so much thicker than Am. Chamusseti 

 as to be nearly globular. The outer whorl entirely envelops the umbilicus; 

 and the keel, which is not crenulated, is nearly obsolete. 



" [P. 15.] Plate II. Fig. 4a. Am. hyperbolicus, Leckenby 

 (Simpson, MS.) side view ; half nat. size. 4b. Front view, showing 

 aperture. 

 " Ammonites hyperbolicus (p. 12). Locality. Red Cliff. 



Remarks 



Proportions, 78, 56, 109, ; subextremiplatygyral, ultraper- 

 extremipachygyral, clausumbilicate. 



Stages, conch, sphaerocone ; periphery, 2c ; ornament ic, though 

 with traces of obsolete subcostse. 



The specimen is without test. Nearly all the outer whorl is body- 

 chamber, and there are no suture-lines traceable. There appears to be 

 no umbilicus, and with test present there would presumably be a 

 columella. 



The keel is represented by a median ridge. There are signs of ribs 

 running at right angles to, and passing over the stout but little elevated 

 keel. Each side of the keel there is a narrow depression. Beyond 

 this is a slight longitudinal ridge. There is a faint sign of another ridge 

 nearer the centre. 



The characters in the above paragraph indicate the generic position — 

 that the species is a catagenetic, sphaeroconic, occlusal development 

 of the series of Am. pustulatus (see S. Buckman, Q.J.G.S. 1913, 164) ; 

 the ridges are the remains of, and occupy the positions of the lines of 

 tubercles seen in those species ; and so the keel may be regarded as the 

 degenerate relic of the crested carina. 



Genus, Phlycticeras, Hyatt, 1900, 569; family, Oppelidse. 



Geological position: from a brown very oolitic matrix with small 

 grains, being one of the beds of Leckenby's Kelloway Rock. (See 

 S. Buckman, 1913, 154). 



Result 

 Phlycticeras hyperbolicum, Simpson - Leckenby sp. 1859, 

 Callovian, koenigi zone, Red Cliff, Scarborough. 



