parti] op tse shalEs-with-'beef.' 87 



There appears to be good foundation for Mr. S. S. Buckman's l 

 conclusion that dissimilar faunas in general are the results of 

 deposition at different dates. Of course, the same species, in 

 various localities and under different conditions, may undergo 

 alterations in characters and size, and when there is isolation, a 

 stock may develop special local features. 



Isolation suggests itself as a cause for a development like 

 Slatte kites slatteri (Wright) (gen. nov., genotype: Natural 

 History Museum, C 6091 = Wright, pi. 1, figs. 1-3, 8), which takes 

 on a broad venter after an oxynote periphery; but the (oxynotus) 

 horizon of this form is doubtful, and it is still possible that it may 

 not be of the age of supposed contemporaneous beds in Dorset or 

 Yorkshire. On the other hand, in the Micraster cor-testudinarium 

 Chalk of England, ammonites are unknown, whereas they occur in 

 the same Chalk in the North of France; and I have pointed out 

 elsewhere 3 that a study of the distribution and dependence on 

 facies of the two fundamental stocks of ammonites (Lytoceratidae 

 and Phylloeeratidge) will show that ammonites may have a strictly 

 limited horizontal distribution. Thus, the genera Ectocentrites 

 and Derolyioceras, from which Deroceratidae are here considered 

 to be derived, never left the Mediterranean Province ; and, since 

 they persisted throughout Lower Liassic times, it is clear that their 

 absence in North- Western Europe cannot be due to 'stratal failure.' 

 For the majority of ammonites, however, difference of facies seems 

 to have little influence on distribution, although it must be remem- 

 bered that recent nectonic forms with highky-developed organs of 

 locomotion may show less inclination to migrate than benthonic 

 mollusca. 3 



Now, between Dorset and Wurtemberg, deposits corresponding 

 in age with those described in the present paper do occur occasion- 

 ally, and probably are represented, for example, in the Upper 

 Gryplicea Beds of Auxerrois and Morvan, whereas the beds with 

 Belemtiites acutus of the neighbourhood of Nancy and of Alsace- 

 Lorraine have been correlated by J. A. Stuber 4 with the tubercu- 

 latus zone in Suabia. In other areas, of course, as, for instance, 

 the neighbourhood of St. Amand (Cher), the fossiliferous zones of 

 the Sinemurian seem to be absent. 5 Failing a continuous sea 

 throughout, there would then have been an archipelago at every 

 emergence and submergence, causing larger unconformities; where- 

 as the local non-sequences and phosphate-beds 6 may be largely 

 due to current-action. Later periods of erosion, however, compli- 

 cate the picture. It should be noted that even in Wurtemberg, 



1 ' Jurassic Chronology : I— Lias ' Q. J. G.S. vol. lxxiii (1917-18) p. 278. 



2 ' On Cretaceous Cephalopoda from Zululand ' Ann. S. Afr. Mus. vol. xii 

 (1921) p. 271. 



3 J. Walther, ' Einleitung in die Geologie, &c.' pt. i (1893) p. 190. 



4 ' Obere Abteilung des Unteren Lias in Deutseh-Lothringen ' Abhandl. 

 Geol. Spez. Karte von Elsass-Lothringen, vol. v (1893) pp. 174-75. 



" A. de Lapparent, ' Traite de Geologie' 5th ed. vol.ii (1906) p. 1116. 

 L. von Werveke, ' Phosphoritzone an der Grenze von Lias a. & /3, &c.' Mitt. 

 Geol. Landesanst. Elsass-Lothringen, vol. v (1903) p. 347. 



