3o6 YORKSHIRE TYPE AMMONITES Mcr. 



30. AMMONITES TURRICULATUS, Simpson 

 (Plate XXX) 



Original Description 

 "75. A[mmonites] turriculatus. [M. Simpson, 1855, p. 59-] 



" I. Without a dorsal keel or furrow." p. 35. 

 " b. Armed with spines or distinct tubercles." p. 58. 



" Volutions 6 or 7, much exposed, outer whorl J the diameter, sides 

 depressed, inner margin prominent, sharply rounded ; radii numerous, 

 fine, annular, pass over the back undivided, with short ones there 

 frequently introduced, on the outer edge of the whorls a row of tubercles 

 or short knobs at intervals of 5 or 6 radii ; aperture subquadrate ; 

 diameter 2J inches. 



" This is rather a robust shell. The radii are fibulated at the 

 tubercles, and nearly obsolete at the ajjerture. — Syn. A. Davaei, Y. & B. 

 [Young & Bird]." 



Additional Details 

 Simpson, 1884, p. 91, adds " U.L." to end of first par. 



Remarks 



Stages, conch, serpenticone ; periphery, i ; ornament, 4c, 4, 5*. 



The plain costate stage lasts to about 35 mm. diameter ; then costae 

 with occasional tubercles making fibulate pattern at rather long intervals. 



The species shows a development of ornament the reverse of that 

 of A. davcei with which it has been confounded, namely 4 to 5 instead 

 of 5 to 4. A. davcei is catagenetic from spinous to costate, this si:)ecies 

 shews anagenesis from costate to spinous. Any suggestion of connecting 

 the two genetically by costate intermediaries of the Dactylioceras pattern 

 must face the difficulty of accounting for the simplified suture line of 

 the Dactyloids. 



As this species has Dactylioceras costation followed by the Peronoceras 

 style of fibulation, it seems to show the origin of the latter genus, and 

 it may be reckoned as an early Peronoceras. It is a connecting link. 



Genus Peronoceras, Hyatt, 1867 (Gen. v) ', family Dactyloidae, 

 Hyatt, 1867. Geological position Upper Lias, with appearance suggesting 

 the Grey Shale, U.L. 8. 



Result 



Peronocer.\s turriculatum, Simpson sp. 1855, Whitbian, [teniii- 

 costatum zone ?], near Whitby. 



