354 L. F. Spath — Jurassic Ammonites from East Africa. 



Till/ S. ovale Pompeckj sp.,''^ and others. On the other hand, in 

 the oldest specimen of Sowerhyceras figured, the Bathonian ;S. 

 Neumayri, the constrictions are typically angular, and the thinness 

 of that specimen only characterizes it as distinct. 



The type of constrictions shown by the specimen here described 

 is found in the group of Phylloceras ultramontanum Zittel, and is 

 well illustrated in e.g. Phylloceras mediterraneum (Neumayr) in 

 Favre,''^ Ph. zignoclianum (d'Orbigny) in Vacek,* and in Ph. Frederici- 

 augusti Pompeckj ,'^ but according to the latter author in this group 

 the first lateral saddle of the internal (dorsal) suture is diphyllic.^ 

 Also, though the suture-line of d'Orbigny's A. zignodianus shows 

 bifid saddles, not unlike those of a Sowerhyceras, the quadrate whorl- 

 section of the East African specimen and the absence of the lateral 

 lappet at the angle of the constrictions are against a closer com- 

 parison with any of the forms of the group of Ph. idtramontanum. 



It is probable that the specimen is most nearly related to the older 

 forms of Sowerhyceras recorded by Neumayr, Parona, and Hochstetter. 

 The former author mentioned (a|)art from the specimen from the 

 Bathonian of Mount Crussol, near Valence, Ardcche, referred to 

 above) a fragment from the Klaus beds of Buscecs, Transylvania,' 

 as the oldest specimen which can be referred to d'Orbigny's species. 

 Hochstetter recorded from the Klaus beds of St. Veit, near Vienna, 

 very small Phylloceras,^ the curious course of the constrictions of 

 which favoured the assumption that they belong to Pompeckj 's 

 " Formenreihe " of Ph. tortisidcatum. Parona recorded his specimen 

 (doubtfully referred to Ph. sidjtortisidcatum Pompeckj ''), together 

 with Lytoceras adeloides and other forms of the Upper Bajocian 

 and Bathonian, from the Posidonomya alpina beds of the Southern 

 Alps. 



Horizon and Distribution. — The group of Phylloceras tortisulcatum 

 (d'Orbigny) ranges from the Bathonian up to the Tithonian, but 



1 Op. cit., 1910, p. 260, pi. xvi (i), figs. 12-14. 



^ Oj). cit., 1893, p. 48, pi. i, figs. 4 and 5. This species is not included in 

 the genus Sowerhyceras by Parona & Bonarelli. 



^ " Descr. Foss. Ter. Jiirass. Mont. Voirons (Savoie) " : Metn. Soc. Pal. 

 Suisse, vol ii, 1875, p. 19, pi. i, fig. 10. In this Argovian form the constrictions 

 are for too deep. 



* Op. cit., 1886, pi. V, fig. 14 only, non pi. iv, figs. 8-10. 



5 Op. cit., 1893, pi. i, fig. 12-14. 



" It may be mentioned that Quenstedt{ Amm. Schwab. Jura, p. 762, jjI. ixxxvi, 

 and p. 864, pi. xciii) had included in A. tortisidcatus both forms put by 

 Pompeckj into the " Formeni'eihe " of PJiylloceras ultramontanu)n, also typical 

 Sowerbyceras. The writer is not inclined to lay too much stress on the course 

 of the constrictions shown to be variable in many other Pfiylloceras. On 

 the other hand, Sowerbijccras is probably a descendant of the Bajocian 

 ultramontanu-t group, as Parona & Bonarelli (loc. cit., p. 117) suggested. 



■^ Loc. cit., 1870, p. 34.5. 



s Loc. cit., 1897, p. 142. 



" De Loriol (loc. cit., 1900, p. 18) was doubtful about the justification of 

 the separation of PJi. .'subtortisulcatum Pompeckj from the typical Ph. 

 tortisidcatum. d'Orbigny sp. 



