103b YORKSHIRE TYPE AMMONITES— II June 



103. AMMONITES SPICATUS, Simpson 

 (Plate CIII) 



Original Description 

 " 46. A[mmonites] spicatus. [M. Simpson, 1843, p. 28.] 



["I. Without a dorsal keel or furrow." p. 7. 

 " b. Armed with spines or distinct tubercles." p. 22.] 



" In the Whitby Museum there is the outer whorl of another 

 [besides A. Hamiltoni], (12 inches in diameter) which I have named 

 A. spicatus. It has had powerful 4 or 5 sided spines, upon the outer 

 edge of the whorl. A small portion of the shell remains, which exhibits 

 none of the annular striae observable in the other armed species ; but 

 on the back of the cast, in some places, I see faint markings running 

 lengthwise, and undulating near the knobs. The aperture appears to 

 have been quadrate, but one side of the shell is entirely destroyed ; 

 it is from the Ironstone beds. There is a mark on the inner part of the 

 whorl, which looks like the impression of a keel. 



There is also in the same Museum about half of another whorl 

 (16 inches diameter), which has the portion near the aperture much 

 flattened, and, at the other end of the segment, the aperture is obtusely 

 triangular, with the apex towards the inner whorl slightly truncated. 

 Near the aperture, the spines are merely tubercles, gradually increasing 

 inwards, with scarcely any appearance of radii. In several places the 

 shell may be seen in very brilliant colours, and on the outside smooth ; 

 but on the inside, are to be observed distinct striae running longitudinally 

 along the back, and undulating near the knobs." 



[Simpson, 1855, 65, 66, and 1884, 98, describes quite a different 

 species — see next article.] 



Remarks 



Proportions, (240, 25, 14, 57) ? substeno-, lepto-gyral ; sub- 

 extremilatumbilicate. 



Stages, conch, serpenticone ; periphery, 1 ; ornament, 5. 



Whorls are broad and thin — the specimen has suffered somewhat 

 from crushing ; aperture somewhat oblong ; spines rather large, rising 

 somewhat suddenly from obscurely costate side ; venter plain, with fine 

 wavy longitudinal lines. 



The type is a fragment from near the end of the body-chamber, 

 as the spines are not septate. It would appear not to be part of so large 

 a specimen as Simpson supposed. 



Genus Deroceras, Hyatt ; family Deroceratidae. Geological position, 

 presumably L.L.y. 



Result 

 Deroceras spicatum, Simpson sp. 1843, Charmouthian, [armatum 

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



