43b YORKSHIRE TYPE AMMONITES Nov. 



25. AMMONITES LECTUS, Simpson 

 (Plate XLIII) 



Original Description 

 " 74. A[mmonites] lectus. [M. Simpson, 1843, p. 34.] 



[" II. With a keel on the back. 

 " a. Outer whorl broad." p. 31.] 



" Much depressed ; volutions 4 or 5, inner ones nearly concealed, 

 outer whorl more than J the diameter ; radii waving, nearly obsolete ; 

 stria numerous, waving ; keel slightly crenated ; diameter i^ inch. 



" The sides of the whorls are regularly convex as in A. ovatus ; 

 the keel is slightly crenated by the radii passing over it, and is little 

 more than the sharp edge of the back, with a slight groove on each side. 

 In this respect, as well as in its general appearance, it greatly resembles 

 A. Boulbiensis, of which I once thought it a mere variety ; but as the 

 inner margin of the whorls is much depressed, so as to leave but a very 

 shallow umbilicus, and as I am not aware that it is ever found in the 

 same beds with A. Boulbiensis, but in others considerably lower in the 

 series, I conclude it to be a distinct species." 



Additional Details 



Simpson, 1855, 75, for " crenated " has " crenulated " in first par. ; 

 then adds " aperture acutely triangular, or ovate " ; in 2nd par. omits 

 remark about " variety " after " Boulbiensis " ; omits " as " after the 

 following " but " ; omits all after " umbilicus." 



Simpson, 1884, no, as in 1855, but adds to end of first par. " U.L., 7." 



Remarks 



Stages, conch, oxycone ; periphery, 3c, concavifastigate ; orna- 

 ment 3c. 



Genus, Pseudolioceras, S. Buckman, i88g ; family Hildoceratidse. 

 The much compressed whorls with shallow, comparatively open umbihcus 

 mark this species as very separable from most other species of the genus. 



Geological position, Simpson says U.L. 7 ( = Jet Rock) ; Blake, 

 1876, 309, zone of A. jurensis. 



Result 



Pseudolioceras lectum, Simpson sp. 1843, fWhitbian, lilli- 

 variabilis zone ? Peak], near Whitby. 



