Vol. 69.] JURASSIC AMMONITES TB.OM JEBEL ZAGHUAN. 575 



and costation distinguishes these later forms. My ammonite does 

 not seem to be a Holcosteplianus ; as the innermost whorls, however, 

 are not shown, it is impossible to make a definite statement on this 

 point. 



Siemiradzki calls A. de Riaz's form a i mutatio descendens' of 

 P. (Grossouvria) minis Bukowski from the cordatus zone of Poland. 

 My specimen may belong to that group of Siemiradzki's Grossouvria, 

 but its many constrictions separate it from P. minis itself. 



Perisphinctes sp. nov., aff. xkichoplocits Gemm. (PI. LIU, fig.' 4.) 



1877. G. G. Gemmellaro, ' Faune Giur. & Liass. della Sicilia ' p. 163 & pi. xx, 



fig. 13. 

 1898. J. von Siemiradzki, ' Monogr. Beschveib. der Amnionitengattung Peri- 



sphinctes' Palaontographica, vol. xlv, p. 273. 



I have not been able to find the description of any ammonite 

 more comparable with my specimen than Gemmellaro's form. 



My specimen differs, however, in having a larger umbilicus 

 (about 50 per cent, at a diameter of 70 mm. instead of 45 percent.) 

 and also a larger number of single costoe. Siemiradzki says that 

 single costse are not frequent, and, as a matter of fact, Gemmellaro's 

 figure shows among eleven costas on the last whorl three single 

 ones ; but in my specimen there are from two to three single ribs 

 between each bifurcating pair, a feature that brings the ammonite 

 very near to certain Simocerates. At a diameter of 60 mm., 

 however, the costse still pass uninterruptedly across the venter, and 

 it is only on the last half of the outer whorl that the sinus, which 

 is formed on the periphery by the meeting of the secondaries, 

 becomes clearly broken in the siphonal line. 



In whorl-section my specimen agrees with Gemmellaro's form, 

 the height from the umbilical junction being a little larger than 

 the width. Only one constriction is visible on my specimen, owing 

 to the umbilicus being partly covered by matrix ; but it is com- 

 paratively broad, as figured by Gemmellaro, and not narrow and 

 shallow as Siemiradzki mentions. 



Genus Peltoceeas Waag. 



Peltocekas toucasiantjm (d'Orb.). (PI. LIT, figs. 5 a & 5 6.) 



1847. A. d'Orbigny, 'Pal. Fran 9. : Terr. Jurass. — Cephal.' p. 508 & pi. cxc. 

 1871. M. Neumayr, 'Jurastudien : 4 — Vertretung der Oxfordgruppe, &c.' Jahrb. 



K.K. Geol. Reichsanst. vol. xxi, p. 368 & pi. xix (xx), fig. 1. 

 1877. G. G. Gemmellaro, ' Faune Giur. & Liass. d. Sicil.' p. 166 & pi. xx, fig. 17. 



The dimensions of my specimen are as follows : — 



Diameter 53 millimetres. 



Height of the last whorl 3rt per cent, of the diameter. 



Thickness of the last whorl 33 per cent, of the diameter. 



Umbilicus 40 per cent, of the diameter. 



Oppel united Quenstedt's Ammonites transversarius with A. d'Or- 

 bigny's form, and Neumayr followed him, although he pointed 

 out that the two ammonites did not quite agree. Neumayr con- 

 sidered, however, that the differences were only apparent, and that 



