566 me. l. p. si?ath on [Dec. 1913, 



Diameter. Height. Thickness. Umbilicus. 



Millimetres. Per cent. Per cent. Per cent. 



20 45 45 25 



21 43 43 25 



21 42 43 26 



22 42 41 27 



23 44 45 22 

 25 45 48 24 



36 42 47 25 



37 46 48 22 



41 44 41 22 



42 43 40 26 



43 44 42 24 



The other specimens are less well preserved. I state the dimen- 

 sions in detail, because they show that, despite some variation, 

 the height of the last whorl is almost equal to the thickness ; 

 whereas in Sowerbyceras tortisulcatum (d'Orb.), which, moreover, 

 belongs to the athleta zone, the proportion of height to thickness 

 is about 4 : 3. This, together with the sharp and high umbilical 

 edge, was the principal distinction in separating the Argovian 

 forms from A. d'Orbigny's ' Oxfordian ' type. 



Pervinquiere records from JebelZaghuan one fragment and three 

 small ammonites, referable to Soiuerbyceras tortisulcatum (d'Orb.), 

 and associated with Ochetoceras arolicum (Opp.) and other Argovian 

 ammonites. They also doubtless belong to the same form as- 

 the specimens here described. 



Sowerbyceras cf. loryi (Munier-Chalmas). 



1876. Ammonites (Phylloceras) silenus Dumortier & Fontannes, ' Descr. des- 



Amra. de la Zone a Amm. tenuilolatus de Crussol ' p. 33 & pi. v, fig. 2. 



1877. Phylloceras silenus in Gemmellaro, 'Faune Giur. & Liass. della Sicilia ' 



p. 185 & pi. xvi, figs. 1-3. 

 1907. Phylloceras loryi in Pervinquiere, 'Etudes de Paleontologie Tunisienue : 

 1 — Cephalopodes des Terrains Secondares ' p. 15 & pi. i, figs. 1-2. 



The two specimens which I refer to this form have the following 

 dimensions : — 



No. 1. No. 2. 



Diameter 37 mm. 33 mm. 



Height of the last whorl 50 49 per cent, of the diameter. 



Thickness of the last whorl ... ?40 43 per cent, of the diameter. 



"Umbilicus 17 18 per cent, of the diameter. 



The narrower umbilicus, with sloping walls and rounded edge,, 

 combined with the absence of constrictions, seems to separate 

 these two ammonites from Sowerbyceras protortisulcatum (Pomp.). 

 Since the specimens are not very well preserved, however, the 

 identification must remain doubtful ; and, in view of the fact that 

 I collected a great number of Sowerbycerata and other forms of 

 the transversarius zone at the same place, I hesitate to assume 

 a later age for these two imperfect specimens. 



Pervinquiere mentions one specimen of Soiverbyceras loryi 

 (Mun.-Ch.) from Zaghuan ; but, near the neighbouring Jebel Ben 

 Saidan, he collected some twenty specimens of S. loryi in the- 



