25b YORKSHIRE TYPE AMMONITES Mar. 



25. AMMONITES DEPRESSUS. Simpson 

 (Plate XXV) 



Original Description 



" 74. A[mmonites] depressus. [M. Simpson, 1843, p. 40.] 



I" II. With a keel on the back. 

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



" Very much depressed ; volutions 4 or 5, inner ones nearly ^ con- 

 cealed, outer whorl ^ the diameter, sides flatted ; radii on the inner 

 whorls straight, prominent, equal to the spaces l:)etween, obsolete on 

 the outer whorls ; striated ; keel strongly crenated ; diameter 2 inches. 



" This ammonite is the most depressed of any I have seen, not even 

 excepting A. lenticularis. The inner whorls diminishing very little in 

 thickness, it has a very shallow umbilicus ; the keel has the cord-hke 

 appearance observed in A. Stokesi, of which I once supposed it to be 

 a variety, but on account of its very depressed form, and the absence 

 of radii from the outer whorl, I am obliged to consider it a distinct species. 

 It also resembles some varieties of A. Clevelandicus, but the septa are 

 much more distant, and their ramifications much more simple, a circum- 

 stance which shews it to be a distinct species ; it i.-, from the ironstone 

 bands." 



Additional Details 



Simpson, 1855, 82, omits ' it is from the ironstone bands " ; 1884, 

 118, 119, for "Stokesi" puts " margaritatus " (iig). 



Remarks 



Stages, conch, oxycone ; periphery, 3c crenate ; ornament, 4c to ic, 

 mainly ic. 



The genus is Amaltheus, Montfort ; family Amaltheidae ; and the 

 geological position perhaps about with .4. clevelandicus as recorded by 

 Simpson, s to n, p. xvii ; but it may be higher. 



Ammonites amaltheus depressus, Quenstedt, Jura, xx, 14, is quite 

 distinct. 



Result 



Am.\ltheus depressus, Simpson sp. 1843, Domerian, [margaritatum, 

 or algovianum zone], near Whitby. 



