part 1] JURASSIC CHRONOLOaT : LIAS. 73 



Table III. — Zonal Succession according to Oppel. 1 



Davceibett. 



Ibexbett. 



Jamesonibett. 



Hauptlager der Terebratula numismalis placed at the top of 

 the Jamesonibett and Rhynchonella thalia given as one of its 

 fossils. 



Oppel (p. 165) quotes Ammonites taylori with and under 

 A. jamesoni, and states that he found it in Northamptonshire. 



Quensteclt gives a little more information of the sequence in 

 his later work (' Ammoniten des Schwabischen Jura ' vol. i, 

 1883-85) which I epitomize thus : — 



Table IV. — Lias y (Wurtemberg) Succession, after Quenstedt,' 2 



EPITOMIZED. 



5. Kalkbank. Ammonites davcei 



4. 



be 



*~ Ammonites jamesoni. 

 (May sometimes appear earlier, and is also 

 found above A. davcei.) 



3. id "l Matrices [Platypleurocerasj. 



2. 



« 



Ammonites taylori. 



(In the lowest layer of the Numismalis- 

 i^ mergel.) 



1. Cymbienbank. Ammonites armatus nodogigas. 

 Small Spirifers. 



These tables of Quenstedt are noticed, because they seem to 

 teach some interesting lessons : they show that the interpretation 

 of openings in different places may easily lead to crisscross correla- 

 tion, especially if there be faunal repetition and also various 

 non-sequences. But also there is nomenclature failure, for he has 

 mistaken species of Platypleuroceras for Wptonia {jamesoni). 

 And the tables show that, when many forms are united under one 

 name, it becomes quite misleading to put them in a stratigraphical 

 table without saying which forms exactly are intended. The 

 greater the generic and specific precision in nomenclature the more 

 exact such tables hecome and can be made ; but, of course, the 

 ideal is to be able to state precisely the position of actual figured 

 specimens : this enables later workers to form their own estimates. 

 From the present point of view, Quenstedt may be said to have 

 missed many opportunities of recording the exact position of his 

 wonderful series of figured Jurassic ammonites, 3 because he did not 



1 XIII, p. 117. 2 XV, 2, vol. i, p. 200. 



3 So far as Jurassic ammonites are concerned, South- Western England 

 (Wessex) is a worthy rival of South- Western Germany (Wiirtemberg), though 

 the English species have not yet received anything like adequate illustration. 

 In two respects the English Jurassic species surpass the German — one in 



