Vol. 69.] JURASSIC AMMONITES FROM JEBEL ZAGHTJAN. 579 



group becomes an absolute necessity if tbe specific distinction of 

 P. fouquei from P. toucasianum is to be definitely established. 

 Taking Neumayrs fig. 1 of pi. xix as an example of a large 

 P. toucasianum, we notice that the costae are not yet radial at 

 the end, and it appears that P. fouquei is distinguished only by 

 an earlier appearance of subrecti- and then recticostation. In all 

 forms of P. fouquei the section is very nearly rectangular. 



I have to describe here two fragments of chambered whorls, 

 measuring respectively 18 and 16 mm. in height. The first agrees 

 in its perfectly straight and radial costation, low umbilical edge, 

 and flat sides with Pervinquiere's figure. The second has its 

 costse slightly curved, but shows a low umbilical rim and otherwise 

 close agreement, though it might possibly more correctly be 

 included in P. fouquei. 



The occurrence of all these forms together at Sidi Bu Gubrin is 

 a significant fact. I am inclined to think that not only P. toucasi- 

 anum, the transversarium-like forms, and their close ally P. fouquei, 

 but also P. pervinquieri occur in Argovian deposits. The latter 

 two may have persisted at least in bimammatum times ; this would 

 account for their occurrence in the transversarius zone of Algeria 

 and Sicily, and in higher beds in Andalusia and elsewhere. 



Genus Aspidoceras Zittel. 



ASPIDOCERAS Cf. ^GIR (Opp.). 



1863. A. Oppel, ' Ueber Juvass. Amm; Pal. Mitt. Mus. d. K. Bayerisch. Staates, 



p. 226 & pi. lxiii, fig. 2. 

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



Jahrb. K.K. Geol. Beichsanst. vol. xxi, p. 372 & pi. xx, fig. 2, pi. xxi, 



fig. 2. 



1 refer, with some hesitation, a small specimen of Aspidoceras 

 to this form, because the latter is so common a fossil in the 

 transversarius zone and has also been recorded (by Baltzer) from 

 Jebel Zaghuan before. As Oppel points out, it is distinguished 

 from what has generally been considered on the Continent as 

 Aspidoceras perarmatum (Sow.) by flatter sides and the earlier 

 appearance of the umbilical tubercles ; but, at the diameter of my 

 specimen (about 18 mm.), which, besides, is not very well preserved, 

 distinction from other similar Aspidocerates is impossible. 



In its quadrate section the ammonite in question also resembles 

 Aspidoceras faustum Bayle 1 and A. ruppelense (d'Orb.), as figured 

 in the ' Paleontologie Prancaise' 2 and by Thurmann 3 : in the adult, 

 only, however. The young of the latter ammonite is much too 

 spinous, and in A. faustum the inner whorls are smooth, not costate. 



Certain small ammonites in my collection from the Ampthill Clay 

 of St. Ives (Huntingdon), which I have referred to A. babeanum 

 (d'Orb.), seem to be distinguished from the Tunisian ammonite 



i 'Expl. Carte Geol. France' vol. iv (1878) pi. xlvii, fig. 1. 



2 'Terr. Jurass— Oephal.' p. 53S & pi. ccv, fig. 2. 



3 J. Thurmann & A. Etallon, ' Lethasa Bruntrutana ' 1861, p. 78 & pi. ii, 



