Vol. 69.] JURASSIC AMMONITES FROM JEBEL ZAGHTJAN. 577 



from Torri, Lake of Garda (Neumayr, pi. xix, fig. 1), at 110 mm. 

 diameter shows : — 



Umbilicus 42 per cent, of the diameter. 



Height of the last whorl 33 percent, of the diameter. 



Quenstedt's type of transversarius, on the other hand, at 45 mm. 

 diameter has : — 



Umbilicus 355 per cent, of the diameter. 



Height of the last whorl 40 per cent, of the diameter. 



The largest figured specimen of a true transversarius (figs, la & 

 7 b of Salfeld) is only fragmentary, aud comparison of measurements 

 in the adult is, therefore, impossible ; but the persistence of the 

 close, slightly curved rursicostae and the trapezoidal section are 

 still very characteristic. 



Neumayr's fig. 1 a, at a diameter of 70 mm., represents the 

 peculiar sigmoidal curvature of the costae, which, as well as being 

 so conspicuous a feature of A. d'Orbigny's type, is well shown in 

 Gemmellaro's figure and is also very distinct on my specimen. It 

 is absent, so far as I am aware, in all the other specimens of 

 ' toucasianum ' or ' transversarium ' figured, and in my opinion 

 clearly distinguishes A. d'Orbigny's form from its descendant, 

 although it remains to be investigated whether the branching of 

 the costae may permit us to recognize several varieties of Pelto- 

 ceras toucasianum. 



The form is characteristic of the transversarius zone of the 

 Mediterranean Middle Corallian, and occurs throughout the Alpine 

 ' geosyncline,' from the Carpathians to Sicily and the range of 

 the Atlas. 



Peltoceras cf. Tor/CAsiANr/M (d'Orb.). 



1906. Peltoceras toucasi (d'Orb.) Salfeld, ' Beitrag z. Kenntnis des Peltoceras 

 toucasi (d'Orb.) & Peltoceras transversarium (Quenst.) ' Neues Jahrb. 

 vol. i (1906) p. 81 & pi. x, fig. 4 only. 



My collection contains only a septate whorl-fragment 21 mm. 

 high, agreeing fairly in ornament with the figure cited above. 

 The costse are simply curved backwards, and form rather strong 

 points at the latero-peripheral angles. The side of the whorl 

 is slightly concave, but the section seems to be distinguished by a 

 broader periphery than is shown, for example, in Salfeld's pi. x, 

 fig. 3 6. My specimen is too fragmentary, however, to enable me 

 to make a closer comparison. 



I may add here that the latero-peripheral angle of the costse is 

 situated in the middle of the outer branch of the external saddle 

 (which is subdivided by a lobule), whereas in whorl-fragments 

 which I refer to the forms described below the end of the costse 

 comes close to the lobule. Thus here the saddle still goes some 

 distance across the venter, showing a broader periphery correspond- 

 ing with a lower umbilical rim. The whole of the suture is not 

 preserved, unfortunately, in any of my specimens. 



The ammonite is neither P. toucasianum nor P. transversarium, 



