i8b YORKSHIRE TYPE AMMONITES Mar. 



i8. AMMONITES CONVOLUTUS, Simpson 

 (Plate XVIII) 



Original Description 

 " 29. A[mmonites] convolutus. [M. Simpson, 1855, p. 43.] 



["I. Without a dorsal keel or furrow. 



" a. No spines." p. 35]. 



" Volutions 5, exposed ; radii strong, waving, rather obliquely 

 inclined towards the aperture, obsolete on the back and inner whorls ; 

 aperture round ; diameter six-tenths in. — L.L., R. H. Bay [Lower Lias, 

 Robin Hood's Bay] " — [Simpson, 1884, p. 73, practically the same]. 



Remarks 



Stages, conch, serpenticone ; periphery, i, almost 2 ; ornament, 4. 



Inner whorls smooth to about 4mm. diam., periphery almost angulate, 

 crossed by forwardly arched ribs and striae — all very faint. Suture line 

 apparently like that of A. belcheri [xvii, 3], but difficult to follow. 



Genus, Caloceras, Hyatt, 1870, 29 ; and family Caloceratidse. 



Geological position presumably just above planorbis-zone. 



Result 



Caloceras convolutum, Simpson sp., 1855, Hettangian, [mega- 

 stonta zone ?], Robin Hood's Bay, near Whitby. 



