5ob YORKSHIRE TYPE AMMONITES Feb. 



50. AMMONITES PERARMATUS, Young cS: I'.mr) 

 (Plate L) 



Original Description 

 [Young & Bird, 1822, pp. 249, 250, 327.] 



" No. II, PI. XIV, is a shell with similar markings |to a. armatiis, 

 PI. XIII, No. q], but of a species quite distinct ; for the spire, instead 

 of being nearly rounded, appears as if gieatly compressed from the back 

 inwards, and the interior shows a deep cavity on both sides, the outer 

 whirls forming a high border around it. Besides, the button and loo]i 

 marking does not give place to plain ribs in the interior part, but con- 

 tinues towards the [p. 250] centre. Its knobs are more strong and 

 prominent than those of the last shell. . . We may call . No. 11. 

 PI. XIV, a. perarmatiis." 



" [P. 327] Plate XIV. Fig. II. Ammonites pcrarmattts. Alum shale." 



Additional Details 



Young & Bird, 1828, p. 263, — " Sowerby has mistaken the 

 A. pcrarmalns of our First Edition for our A. subarmatus, and figured it 

 under the latter name. Tab. 407. i : which name we shall allow it to 

 retain. Its sides are marked in the button and loop style, as in 

 A. fibulatus ; but the whirl is very differently shaped, being greatly 

 compressed from the back inwards, and rapidly diminishing in thickness : 

 the central part on the side forming a deep cavity, round which the 

 outer whorl rises like a high ridge, often surmounted with strong spines, 

 as in Sowerby's A. Listeri, Tab. 501. i. We have figured this shell, 

 which we shall now call A. subarmatus, PI. xiv, .\o. 8. It is not plentiful, 

 and at the same time it admits of varieties ; the sides varying in Ihcii 

 depth, and the knobs and ribs in their sharpness and prominence." 



Remarks 



Stages, conch, serpenticone ; periphery, i ; ornament. 5*. The 

 ]ieriphery is, in part, abraded. In the somewhat crateriform umbilicus 

 there is only a trace of fibulation ; ornament otherwise is regularlv 

 tuberculate. 



Genus, Porpoceras (Gen. 77) ; family, Dactyloidas. Hyatt, 1867: 

 In the same year, 1822, in June, the title Ammonites perarmatus 

 was given by James Sowerby to a species [Aspidoceras'] " found in the 

 PisoHte fCorallian] of Malton [Yorkshire] — M. C. iv, 72. In p. 146, 

 footnote, May, 1823, J. de C. Sowerby says " We had not seen the Geol. 

 of the Yorkshire coast, when A. perarmatus, tab. 352 was published." 

 This seems to imply that Young & Bird's work was published first, and 

 that their A. perarmatus takes precedence. However, as the names are 

 homonyms, not synonyms, and the genera are now distinct, both the 

 trivial titles can remain. 



' Result 



Porpoceras per.\rm.\tum. Young Si Bird sp, 1822, Whitbian, 

 \fihrdatmn zone, near Whitby]. 



