8ob YORKSHIRE TYPE AMMONITES— II August 



80. AMMONITES PINGUIS, Simpson 

 (Plate LXXX) 



Original Description 

 " 186. A[mmonites] pinguis. [M. Simpson, 1855, p. 100.] 



[" III. Keel between two furrows." p. 90. 

 " b. Furrows distinct." p. 93.] 



Thickish ; volutions 5 or 6, inner ones \ concealed, outer whorl 

 less than \ the diameter, inner margin nearly perpendicular, sides regularly 

 rounded ; radii numerous, waving, strongest on the outer half of the 

 whorl ; keel plane, obtuse, between two distinct furrows ; aperture ovate ; 

 diameter if inch. 



" This is much thicker than the last [A. latescens, Simp.] ; and 

 the radii more numerous ; the keel also appears to be constructed in 

 a different way, so as to be knocked oft with the shell ; whilst in 

 A. latescens, it remains perfect where the shell has been removed. It is 

 of a brown colour, and shining. It is from the jet-rock of the upper lias. 

 — Mr. Clarkson's Col." 



Simpson, 1884, p. 141, the same, except for trivial typographic 

 details. 



Remarks 



Proportions ( 42 43 36 31 ) 

 I 22 39 47 27 I 



Stages, conch, somewhat platycone ; periphery, 5 ; ornament, 3c 

 to 4c. 



The whorls are only slightly gibbous, the ribs are small and numerous, 

 unequal in size (irregular in strength), tending to be connate towards 

 the steep, subconcave, plain umbilical margin, while some fail towards 

 the inner area. 



The keel which Simpson noted is really constructed on the same 

 plan as that of A. latescens (No. 79), being a septicarina, but the test 

 is on the periphery where the keel has been removed, and so the partition- 

 band is flush, and does not show a false keel. In places the keel is partly 

 preserved, and towards the end of whorl it is complete : it is then small, 

 but well defined, and subacute. 



Genus Whitby icer as, no v. (II, v) ; family Hildoceratidae, subfamily 

 Hauginae. , 



Geological position, Simpson gives the Jet Rock, but this is doubtful 

 if the species is correctly interpreted as an ally of Brodiceras : it would 

 be expected in strata of similar geological age to its allies, namely lilli 

 or variabilis zones. 



Result 



Whitbyiceras pingue, Simpson sp. 1855, [Whitbian, lilli-variabilis 

 zone ? Peak, near Whitby.] 



