Yol. 69.] JURASSIC AMMONITES FROM JBBEL ZAGHUAN. 547 



Jebel Zaghuan appear to indicate the incoming of a different facies 

 at the top of the Jurassic System. 



It remains only for me to acknowledge very gratefully my 

 indebtedness to the officials of the Geological Department of the 

 British Museum (Natural History) for facilities afforded during 

 the examination of the specimens in their charge ; and to express 

 my great obligation to Dr. A. Morley Davies and Mr. C. P. Chatwin, 

 for kindly looking through this paper and offering valuable 

 suggestions. 



III. Description oe the Ammonites. 



(1) LIAS. 



Family Hildoceratidse Hyatt em. S. Buckman. 



Protogrammoceras, gen. nov. 



A brief explanation is necessary in justification of the establish- 

 ment of this new genus. 



The present state of the classification of the Domerian Hildo- 

 ceratidse is unsatisfactory. Most authors either group the forms 

 which are here considered with ammonites of later lineages, but 

 similar external appearance, or else refer them to the convenient 

 though much-abused genus Harpoceras, sensu latissimo. 



A few examples may be mentioned. Prof. Haug ' quotes the 

 typical rectiradiate Domerian Seguenziceras algovianum (Opp.) 

 alternately as Grammoceras and Harpoceras, which, in turn, also 

 are used to accommodate A. d'Orbigny's Ammonites normanianus. 

 A. Fucini, 2 again, places the latter in Hildoceras, also a strictly 

 Toarcian genus ; and P. Rosenberg 3 restricts the genus Harpoceras 

 to forms with a carinatisulcate periphery, although that genus had 

 already been restricted by Mr. Buckman to the true Toarcian falciferi 

 twenty-two years earlier. 4 On the other hand, Dr. Rosenberg 

 identified a Middle Liassic sickle-ribbed form with Grammoceras 

 fallaciosum Bayle from the jurense zone, whereas it is not difficult 

 to see that Bayle's excellent figure 5 is distinguished by a particular 

 straightness of the costae on the lateral area. 



The present desideratum is a genus in which to place the am- 

 monites collected at Zaghuan. Unfortunately, the material is very 

 scanty, and even in the British Museum collections Mesoliassic 

 Hildoceratidse are almost unrepresented, wherefore an original 

 study of the sutures, inner whorls, and probable septate character 

 of the carina could not be carried out. On the other hand, it is not 



i 'Traite de Geologie ' vol. ii (1908) pt. 2. 



2 ' Cefalop. Liass. del Mte. di Cetona ' pt. 5, Pal. Ital. vol. xi (1905) p. 108. 



3 ' Liasische Cephal. -Fauna d. Kratzalpe ' Beitr. Palaont. & Geol. CEsterr.- 

 Ung. vol. xxii (1909) p. 304. 



4 Geol. Mag. dec. 3, vol. iv (1887) p. 397. 



5 ' Expl. Carte Geol. France ' vol. iv (1878) pi. lxxviii, figs. 1 & 2. 



