.Ub YORKSHIRE TYPE AMMONITES Apr 



31. AMMONITES SEMICELATUS, Simpson 

 (Plate XXXI) 



Original Description 

 " 32. A[mmonitesJ semicelatus. [M. Simpson, 1843, p. 22.] 



[" I. Without a dorsal keel or furrow. 

 " a. No spines." p. 7.] 



" This agrees very nearly with the last [A. annulatus, Sowerby] ; 

 but the inner whorls are nearly one-half concealed by the outer whorl. 

 There are others which have often been confounded with this, but I would 

 rather consider them as varieties of the last, or compressed specimens of 

 A. communis, and restrict the present name to those which have the 

 inner whorls somewhat concealed." 



Additional Details 



Simpson, 1855, pp. 50, 51. — " 54. A. semicelatus. — Depressed ; 

 volutions 7 or 8, inner ones nearly J concealed, outer whorl more than 

 ^ the diameter, inner margin depressed, depressed 1 p. 51] near the 

 back ; radii annular, pass nearly straight over the back, rounded, fine, 

 numerous, equal to the intervening concave furrows, double in number 

 on the back ; aperture ovate ; diameter 3^ inches. 



" The form of the radii and the smoothness of the cast render this 

 species very like a compressed variety of A. annulatus ; but it may be 

 distinguished by the greater width of the outer whorl, partly concealing 

 the inner ones, as well as by its more depressed form. 



" On the inner whorls the margin is prominent ; radii regular, distinct, 

 split in two near the back, flatted, separated by concave spaces ; radii of 

 the cast round aperture ovate — U.L." 



Simpson, 1884, pp.81 82; places "the" before " aperture " in last 

 par. (p. 82). 



Remarks 



Stages, conch, serpenticone ; periphery, i ; ornament, 4 (4c ?). 



Costse septate ; whorls convergent. No tubercles visible on costse. 

 Genus, Dactylioceras, Hyatt, 1867 (Gen. v). Family, Dactyloidw, Hyatt, 

 1867. Geological position i^ " zone of A. angulatus " [anntdatus], Blake, 

 1876. 299, = Grey Shale, U.L. 8. 



Result 



Dactylioceras semicelatum, Simpson sp. 1843, Whitbian, ienui- 

 costatttm-zone, near Whitby. 



