102b YORKSHIRE TYPE AMMONITES— II Mar. 



104. AMMONITES HASTATUS, Young & Bird 

 Plates CIIa, b. 



Original Description 

 [Young & Bird, 1828, pp. 261, 262, 359.] 



[P. 261.] " No. 3, PI. xiv, is another rare ammonite that comes 

 near to Sowerby's A. armatus, particularly in having striated spines ; 

 the striae on the sides converging (as described by him) towards the 

 apex of each spine, and then diverging from it across the back : but in 

 other respects it differs greatly from what he describes ; for though it is 

 a young, or at least a small shell, it is so far from being " plain and without 

 the spines," that it has very long spines, where they are entire, continued 

 on the interior whirls, and gradually diminishing to the centre ; nor do 

 they bend over the back, as shewn in Sowerby's figure, but rise from the 

 sides nearly at right angles. The aperture is transversely ovate, the 

 whirl being much broader on the back than on the side. The long [p. 262] 

 spine, No. 4, is attached to a fragment of a larger ammonite of a similar 

 shape, which has 'probably been of this species. The spine appears to 

 have been, when entire, about two inches long, so that the ammonite 

 furnished with rows of such spines would have a very formidable aspect. 

 To this species we may give the name A. hastatus ; leaving the title 

 A. armatus to No. 2, [PI. xiv], as coming nearest to that so called by 

 Mr. Sowerby." 



[P- 359-] " Plate XIV. Ammonites. P. 258, etc. 

 Fig. 



3. A. hastatus. Ditto. [Lias bands.] 



4. Fragment of ditto with a long spine. Ditto." 



Additional Details 

 Simpson, 1855, p. 65. — " 92. A. hastatus, Y. & B. . . diameter 

 6 in[ches] . . . L.L. ; R. H. Bay." 



Remarks 



Proportions, 153, 23, 29, 58 ; substeno-, subpachy-gyral ; sub- 

 extremilatumbilicate. 



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



Whorls obtrapeziform ; rugosities leading to spines not pronounced ; 

 over all small rib-like markings which are strong and distinct on the 

 slightly arched venter. About three-eighths whorl is body-chamber, 

 with 5 spines all septate, but the last rises much before showing septum ; 

 the septum is on the top of what is shown as spine. 



The example now illustrated is the original of Simpson's description : 

 it also agrees well with Young & Bird's description, particularly in regard 

 to the direction of the spines. One difficulty is the use of the words 

 " small shell." This, however, may be relative : as allied species attain 

 a diameter of 16 inches and more, this example might merit the title 

 small shell in distinction. Compared with their figure, it shows^ fewer 

 spines, but the costate venter agrees. 



Genus, Deroceras, Hyatt ; family Deroceratidae. Geological position, 

 presumably with the other armati. 



Result 

 Deroceras hastatum, Young & Bird sp. 1828, Charmouthian, 

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



