546 mr. i. f. spate: on [Dec. 19 13, 



ammonites, the dimensions of which agree fairly well with the 

 type — occurred together with a very large number of specimens 

 of Sowerbyceras protortisulcatum (Pomp.), and although S. loryi 

 has been quoted from various horizons, it certainly occurs in beds 

 higher than the Argovian. Yet Pervinquiere mentions already x 

 the singularly close resemblance of one of his fragments to S. loryi, 

 although Munier-Chalmas was of opinion that the specimens 

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

 ammonites) belonged to S. tortisulcatum. As Pervinquiere says, 

 the two forms are indeed closely allied ; and, since the differences 

 do not seem so constant as has been made out, there will often be 

 great difficulty in the distinction. This case, then, is similar to that 

 of Peltoceras fouquei Pervinq. non Kil., which is found with the older 

 P. toucasianum and P. transversarium and an intermediate form. 



It may be added that Pervinquiere mentions also a true 

 Soiverbyceras loryi from Zaghuan ; but the evidence, like that of 

 Simoceras cf. doublieri (d'Orb.), 2 a doubtful impression in red 

 limestone, does not appear strong enough to warrant the attribution 

 of these forms to the Lower Tithonian with certainty. Until 

 the relations have been more clearly determined, the presence 

 of the ' acanthicus ' beds, which would include both the Upper 

 Kimmeridgian and the Lower Tithonian, cannot be considered as 

 proved beyond doubt. Their presence is quite probable, since, on 

 the neighbouring Jebel Ben Saidan, similar red limestones with 

 undoubted ' acanthicus' forms occur; but it should be pointed out 

 that the distinction between the so-called ' Lower Tithonian ' 

 and the Argovian is a matter of great difficulty with the material 

 that is at present at our disposal. 



(4) Conclusions. 



The absence in the Tunisian Atlas of all strata intervening 

 between the Middle Lias and the Argovian has generally been 

 regarded as an established fact. The presence of the Callovian, 

 however, necessitates some modification of that view. The Middle 

 Jurassic transgression began in Callovian times, since deposits of 

 that age probably rest directly on the Domerian. The latter has 

 now yielded typical ammonites, but the question as to whether the 

 Toarcian is completely absent must remain undecided. 



Whether the higher beds of the ' Oxfordian ' are represented or 

 have, perhaps, been cut out by the extensive faulting, of which the 

 general calamitization seems to afford proof, so that the Middle 

 Oolitic succession may be more complete than we think, or whether 

 new transgressions in Argovian and Upper Kimmeridgian times 

 brought back the sea and exactly similar deposits of red ammonitic 

 limestones, it is impossible to say at present. 



The Ellipsactinia Limestones which have been recorded from 



1 'Etudes de Paleontologie Tunisienne : I — Ceplialopodes des Terrains 

 Secondares ' (1907) p. 15. 



2 Ibid. p. 29. 



