56 MISS MAUD HEALET ON [Feb. I9O4, 



Many figures and descriptions of the changes which P. plicatilis 

 undergoes as it grows bigger have been published : but as I have not 

 yet seen the form which I should feel justified in calling the adult 

 of this species, I must for the present content myself with a de- 

 scription of the f type '-specimen. 



Locality and Stratigraphical Position. — Unfortunately, 

 no precise record of the locality whence this ' type ' came has been 

 preserved. Sowerby contented himself with the indefinite state- 

 ment that it is found in a 



' sandy stratum containing beds of sandv limestone at Drv Sandford and 

 Marcham. N.W. of Abingdon.' l 



It is, however, undoubtedly an Upper Corallian form, and is usually 

 taken as the zone-fossil of that horizon. 



Affinities and Differences. — Ammonites plicatilis, as figured 

 by Alcide d'Orbigny, 2 is more evolute and more compressed than 

 the type, while his figures on pi. cxci are Perisphinctes bipleso accord- 

 ing to Dr. Siemiradzki, that is, P. variocostatus (Buckl.). Dr. Siemi- 

 radzki regards Am. biplex as figured by d'Orbigny, 3 and P. plicatilis 

 as represented by Waagen, 4 as synonymous with P. orientalis, Siem. 

 They differ from Sowerby's ' type ' plicatilis in being more evolute 

 and more compressed, but they are much nearer to it than the 

 figures in ' Paleontologie Franeaise.' A. de Riaz 5 takes d'Orbigny's 

 fig. 1, pi. cxcii, as the type, aud consequently the specimen that he 

 regards as typical G is more evolute and slightly more compressed 

 than the real plicatilis : it is also distinguished by fewer and more 

 pronounced constrictions. De Eiaz further states that he agrees with 

 Favre in his interpretation of this species ; but the latter s figures 7 

 appear to me to be quite different, inasmuch as they have rounder 

 whorls, and their ribs are stronger, fewer in number, and bifurcate 

 sooner. De Eiaz does note the last point. 



Perisphinctes Martelli, Oppel. approaches our ' type ' very closely. 

 I am accepting Dr. SiemiradzkiV views on P. Martelli, as he is 

 acquainted with Oppel's original specimens. He takes fig. 3, pi. lv, 

 of Waagen (op. cit.), as representing it, and puts pi. cxci, d'Orb. Pal. 

 Franc., Ter. Jur. vol. i (which OppeP quotes as the 'type' of his 

 species), with P. hiplex (Sow.). The suture-line which he delineates 

 differs from that of P. plicatilis (Sow.) in the character of the 

 terminal branches of the siphonal lobe, and in having one auxiliary 



1 « Mineral Conchology ' vol. ii (1818) p. 149. 



2 Pal. Franc. ' Terrains Jurassiques ' vol. i (1849) pi. cxcii, figs. 1 & 2. 



3 Murchison, De Verneuil, & Keyserling. 'Geologie de la Kussie d'Europe & 

 des Montagnes d'Oural ' vol. ii (1845) pi. xxxvii, figs. 3 & 4. 



4 Mem. Geol. Surv. India, Palaeontologia Indica, ser. ix, ' Jurassic Cephalo- 

 poda of Kutch ' vol. i (1875) pi. Ii, figs. 2 a & 2 6. 



5 ' Description des Ammonites des Couches a Peltoceras transversarium 

 (Oxfordien superieur) de Trept (Isere) * Lvons-Paris, folio, 1898. p. 10. 



6 Ibid. pi. iii. fig. 1. 



7 Mem. Soc. Pal. Suisse, vol. ii (1875) ' Description des Fossiles du Terrain 

 jurassique de la Montague des Voirons ' pi. iii, figs. 1-3. 



s Palaeontographica, vol. xlv (1898) p. 267. 



9 Pahcontologische Mittheilungen aus dem Museum des kgl.-bayerischen 

 Staates : ' Ueber jurassische Am in on i ten ' 1862, p. 247. 



