Yol. 69.] JURASSIC AMMONITES FROM JEBEL ZAGHUAN. 573 



Perisphinctes cf. sayni De Riaz. 



1898. A. de Riaz, ' Descr. des Amm. des Couclies a Peltoceras transversarium 



de Trept (Isere) ' p. 18 & pi. xv, fig. 5. 



1899. J. von Siemiradzki, ' Monogr. Beschreib. der Amnioniteiigattung Peri- 



sphinctes ' Palseontographica, vol. xlv, p. 309 & fig. 75. 



One of my small ammonites agrees with De Riaz's figure, but 

 this represents only the outer whorl of a large specimen. 



According to Siemiradzki, the inner whorls have a depressed 

 quadrate section and strong straight costa?, ^which bifurcate into 

 much weaker branches on the ventral area. My specimen agrees 

 in these particulars very well. Pseudotrifurcation is also shown, 

 and altogether the shell has somewhat the aspect of an annulose 

 Peltoceras, or, as De Riaz says, if the costae did not branch, of 

 Simoceras. 



My form seems to differ in not having the costae as close as the 

 type (sixty costse per whorl, according to Siemiradzki), but this 

 difference might be accounted for by its small size, especially as a 

 fragment of a younger whorl depicted by A. Borisyafe 1 shows ribbing 

 of a character exceedingly like that of my specimen. 



Perisphinctes cf. jelskii Siem. 



1887. Ammonites eonvolutus Quenstedt, ' Ammoniten d. Schwabischen Jura' 



pi. xciv, fig. 8. 

 1898. Perisphinctes jelskii Siemiradzki, 'Monogr. Beschreib. d. Ammoniten- 



gattung Perisphinctes' p. 274 & pi. xxiv, fig. 36 only. 



My specimen has unfortunately only the ventral region well 

 preserved, and comparison with the above figures, which represent 

 lateral views, is difficult. The ventral sinus described by the 

 secondary costas on the periphery and the almost grooved siphonal 

 line are shown in fig. 40 of Quenstedt's pi. xciv. But this 

 form (also called A. eonvolutus by Quenstedt) is referred by 

 Siemiradzki to P. obliqueradiatus Yiissen, and in that lineage 

 ( Ataxioeeras-lotliari group) no parabolar markings are developed, 

 whereas my specimen shows about six pairs of knobs per half-whorl. 

 It is on account of these parabolar markings that I refer my 

 specimen to P. jelskii Siem., a form in which the young whorls 

 have a similar depressed section, with strong prorsiradiation and 

 constrictions. 



P. jelslcii Siem. occurs in the transversarius zone of Poland, 

 Swabia, and Prance. 



Perisphinctes plicatilis De Riaz (non Sow. nee Siem.). 



1898. A. de Riaz, ' Descr. des Amm. des Couches a Peltoceras transversarium 



de Trept (Isere) ' p. 9 & pi. iii, figs. 1-4. 



1899. J. von Siemiradzki, ' Monogr. Beschreib. der Ammonitengattung Peri- 



sphinctes ' Palseontographica, vol. xlv, p. 343. 



One specimen, consisting of about three-quarters of an ammonite 



1 ' Fauna des Donez-Jura : I — Cephalopoda ' Mem. Com. Geol. Russie, n. s. 

 No. 37, 1908 : ' P. sayni, de Riaz ' p. 75 & pi. vi, fig. 1, pi. ii, figs. 15-17. 



