n 7 b YORKSHIRE TYPE AMMONITES— II Dec. 



117. AMMONITES GREGARIUS, Bean-Leckenby. 

 (Plates CXVII A, b) 



Original Description 

 [Leckenby, 1859, PP- 7> IJ ] 



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

 Ammonites gregarius ? Bean, MS. 



" [P. 11] 22. Ammonites gregarius (?), Bean, MS. 



" Except in its greater comparative thickness, which renders the 

 umbilicus deeper, and the somewhat more robust character of the ribs, 

 I cannot distinguish this from Am. fiexicostatus. 



" Locality. South side of the Castle Rock, Scarborough. 



Proportions :- 



(5i, 



' (79> 



Remarks 



32, 25, 38. 



79» 33> 32, 40- 

 II, 81, 36, 29, 35. 



Stages, conch, serpenticone ; periphery, ic ; ornament, 4. 



There are two examples in the Sedgwick Museum, Cambridge, 

 regarded as the types of this species. One (No. II above) bears a label 

 in Bean's handwriting " Am. gregarius mihi Scarboro " ; but this gives 

 no reason to conclude that it was definitely selected as the holotype, 

 for such was not the practice on those days : it is a somewhat malformed 

 specimen, due to injury perhaps. The two efxamples are now taken as 

 Syntypes and No. I is chosen as Lectotype. There is about 1 in. body- 

 chamber to this example ; none to the other. 



Whorls in young stage much compressed : after about 60 mm. diam. 

 swollen stage begins, affecting mainly inner area, inner margin becoming 

 prominent and steep — the whorl convergent, in section subtriangular. 

 Ribs markedly prorsiradiate ; expanding ^-pattern (about a right angle) 

 on a narrowish rounded venter — Q-apex slightly swollen in many cases. 

 On outer whorl primaries spaced, more or less distinctly bifurcate ; one, 

 two, sometimes three unattached and unconnected secondaries in the 

 intervals. Suture-line with somewhat short, broad-stemmed lobes, 

 L2 fairly developed, produced to line of lobules of Li : in enlarged photo- 

 graphs (CXVII a, 3 ; b, 2) width of L2 diminished owing to foreshortening. 



Genus, PRORSICERAS, nov. (p. xiv) ; family Cadoceratidse, Hyatt, 

 1900. 



Geological position : from a bed of Leckenby 's Kelloway Rock, 

 matrix bluish, calcareous, having many close-packed fairly large oolite 

 grains (S. Buckman, 1913, 153). 



Result 

 Prorsiceras gregarium, Bean-Leckenby sp. 1859, Drvesian, 

 gregarium zone, Castle Rock, Scarborough, Yorkshire. 



